README.prod.md

Zulip in production

This documents the process for installing Zulip in a production environment.

Note that if you just want to play around with Zulip and see what it looks like, it is easier to install it in a development environment following the instructions in README.dev, since then you don't need to worry about setting up SSL certificates and an authentication mechanism.

Recommended requirements:

• Server running Ubuntu Trusty
• At least 2 CPUs for production use with 100+ users
• At least 4GB of RAM for production use with 100+ users. We strongly recommend against installing with less than 2GB of RAM, as you will likely experience OOM issues. In the future we expect Zulip's RAM requirements to decrease to support smaller installations (see zulip#32).
• At least 10GB of free disk for production use (more may be required if you intend to store uploaded files locally rather than in S3 and your team uses that feature extensively)
• Outgoing HTTP(S) access to the public Internet.
• SSL Certificate for the host you're putting this on (e.g. zulip.example.com). If you just want to see what Zulip looks like, we recommend installing the development environment detailed in README.md as that is easier to setup.
• Email credentials Zulip can use to send outgoing emails to users (e.g. email address confirmation emails during the signup process, missed message notifications, password reminders if you're not using SSO, etc.).

Installing Zulip in production

These instructions should be followed as root.

(1) Install the SSL certificates for your machine to /etc/ssl/private/zulip.key and /etc/ssl/certs/zulip.combined-chain.crt. If you don't know how to generate an SSL certificate, you, you can do the following to generate a self-signed certificate:

apt-get install openssl
openssl genrsa -des3 -passout pass:x -out server.pass.key 4096
openssl rsa -passin pass:x -in server.pass.key -out zulip.key
rm server.pass.key
openssl req -new -key zulip.key -out server.csr
openssl x509 -req -days 365 -in server.csr -signkey zulip.key -out zulip.combined-chain.crt
rm server.csr
cp zulip.key /etc/ssl/private/zulip.key
cp zulip.combined-chain.crt /etc/ssl/certs/zulip.combined-chain.crt

You will eventually want to get a properly signed certificate (and note that at present the Zulip desktop app doesn't support self-signed certificates), but this will let you finish the installation process. You can get a free properly signed certificate from the new Letsencrypt service, by following their nginx instructions.

When you do get an actual certificate, you will need to install as /etc/ssl/certs/zulip.combined-chain.crt the full certificate authority chain, not just the certificate; see the section on "SSL certificate chains" in the nginx docs for how to do this:

(2) Download the latest built server tarball and unpack it to /root/zulip, e.g.

wget https://www.zulip.com/dist/releases/zulip-server-latest.tar.gz
mkdir -p /root/zulip && tar -xf zulip-server-latest.tar.gz --directory=/root/zulip --strip-components=1

(3) Run

/root/zulip/scripts/setup/install

This may take a while to run, since it will install a large number of packages via apt.

(4) Configure the Zulip server instance by filling in the settings in /etc/zulip/settings.py. Be sure to fill in all the mandatory settings, enable at least one authentication mechanism, and do the configuration required for that authentication mechanism to work. See the section on "Authentication" below for more detail on configuring authentication mechanisms.

(5) Run

su zulip -c /home/zulip/deployments/current/scripts/setup/initialize-database

This will report an error if you did not fill in all the mandatory settings from /etc/zulip/settings.py. Once this completes successfully, the main installation process will be complete, and if you are planning on using password authentication, you should be able to visit the URL for your server and register for an account.

(6) Subscribe to the Zulip announcements Google Group to get announcements about new releases, security issues, etc.

Authentication and logging into Zulip the first time

(As you read and follow the instructions in this section, if you run into trouble, check out the troubleshooting advice in the next major section.)

Once you've finished installing Zulip, configuring your settings.py file, and initializing the database, it's time to login to your new installation. By default, initialize-database creates 1 realm that you can join, the ADMIN_DOMAIN realm (defined in /etc/zulip/settings.py).

The ADMIN_DOMAIN realm is by default configured with the following settings:

• restricted_to_domain=True: Only people with emails ending with @ADMIN_DOMAIN can join.
• invite_required=False: An invitation is not required to join the realm.
• invite_by_admin_only=False: You don't need to be an admin user to invite other users.
• mandatory_topics=False: Users are not required to specify a topic when sending messages.

If you would like to change these settings, you can do so using the Django management python shell (as the zulip user):

cd /home/zulip/deployments/current
./manage.py shell
from zerver.models import *
r = get_realm(settings.ADMIN_DOMAIN)
r.restricted_to_domain=False # Now anyone anywhere can login
r.save() # save to the database

If you realize you set ADMIN_DOMAIN wrong, in addition to fixing the value in settings.py, you will also want to do a similar manage.py process to set r.domain = "newexample.com". If you've already changed ADMIN_DOMAIN in settings.py, you can use Realm.objects.all() in the management shell to find the list of realms and pass the domain of the realm that is not "zulip.com" to get_realm.

Depending what authentication backend you're planning to use, you will need to do some additional setup documented in the settings.py template:

• For Google authentication, you need to follow the configuration instructions around GOOGLE_OAUTH2_CLIENT_ID and GOOGLE_CLIENT_ID.

• For Email authentication, you will need to follow the configuration instructions for outgoing SMTP from Django. You can use manage.py send_test_email username@example.com to test whether you've successfully configured outgoing SMTP.

You should be able to login now. If you get an error, check /var/log/zulip/errors.log for a traceback, and consult the next section for advice on how to debug. If you aren't able to figure it out, email zulip-help@googlegroups.com with the traceback and we'll try to help you out!

You will likely want to make your own user account an admin user, which you can do via the following management command:

./manage.py knight username@example.com -f

Now that you are an administrator, you will have a special "Administration" tab linked to from the upper-right gear menu in the Zulip app that lets you deactivate other users, manage streams, change the Realm settings you may have edited using manage.py shell above, etc.

You can also use manage.py knight with the --permission=api_super_user argument to create API super users, which are needed to mirror messages to streams from other users for the IRC and Jabber mirroring integrations (see bots/irc-mirror.py and bots/jabber_mirror.py for some detail on these).

There are a large number of useful management commands under zerver/manangement/commands/; you can also see them listed using ./manage.py with no arguments.

One such command worth highlighting because it's a valuable feature with no UI in the Administration page is ./manage.py realm_filters, which allows you to configure certain patterns in messages to be automatically linkified, e.g. whenever someone mentions "T1234" it could be auto-linkified to ticket 1234 in your team's Trac instance.

Checking Zulip is healthy and debugging the services it depends on

You can check if the zulip application is running using:

supervisorctl status

And checking for errors in the Zulip errors logs under /var/log/zulip/. That contains one log file for each service, plus errors.log (has all errors), server.log (logs from the Django and Tornado servers), and workers.log (combined logs from the queue workers).

After you change configuration in /etc/zulip/settings.py or fix a misconfiguration, you will often want to restart the Zulip application. You can restart Zulip using:

supervisorctl restart all

Similarly, you can stop Zulip using:

supervisorctl stop all

The Zulip application uses several major services to store and cache data, queue messages, and otherwise support the Zulip application:

• postgresql
• rabbitmq-server
• nginx
• redis
• memcached

If one of these services is not installed or functioning correctly, Zulip will not work. Below we detail some common configuration problems and how to resolve them:

• An AMQPConnectionError traceback or error running rabbitmqctl usually means that RabbitMQ is not running; to fix this, try:

  service rabbitmq-server restart
  

  If RabbitMQ fails to start, the problem is often that you are using a virtual machine with broken DNS configuration; you can often correct this by configuring /etc/hosts properly.

• If your browser reports no webserver is running, that is likely because nginx is not configured properly and thus failed to start. nginx will fail to start if you configured SSL incorrectly or did not provide SSL certificates. To fix this, configure them properly and then run:

  service nginx restart
  

If you run into additional problems, please report them so that we can update these lists! The Zulip installation scripts logs its full output to /var/log/zulip/install.log, so please include the context for any tracebacks from that log.

Making your Zulip instance awesome

Once you've got Zulip setup, you'll likely want to configure it the way you like. There are four big things to focus on:

(1) Integrations. We recommend setting up integrations for the major tools that your team works with. For example, if you're a software development team, you may want to start with integrations for your version control, issue tracker, CI system, and monitoring tools.

Spend time configuring these integrations to be how you like them -- if an integration is spammy, you may want to change it to not send messages that nobody cares about (E.g. for the zulip.com trac integration, some teams find they only want notifications when new tickets are opened, commented on, or closed, and not every time someone edits the metadata).

If Zulip doesn't have an integration you want, you can add your own! Most integrations are very easy to write, and even more complex integrations usually take less than a day's work to build. We very much appreciate contributions of new integrations; there is a brief draft integration writing guide here.

It can often be valuable to integrate your own internal processes to send notifications into Zulip; e.g. notifications of new customer signups, new error reports, or daily reports on the team's key metrics; this can often spawn discussions in response to the data.

(2) Streams and Topics. If it feels like a stream has too much traffic about a topic only of interest to some of the subscribers, consider adding or renaming streams until you feel like your team is working productively.

Second, most users are not used to topics. It can require a bit of time for everyone to get used to topics and start benefitting from them, but usually once a team is using them well, everyone ends up enthusiastic about how much topics make life easier. Some tips on using topics:

• When replying to an existing conversation thread, just click on the message, or navigate to it with the arrow keys and hit "r" or "enter" to reply on the same topic
• When you start a new conversation topic, even if it's related to the previous conversation, type a new topic in the compose box
• You can edit topics to fix a thread that's already been started, which can be helpful when onboarding new batches of users to the platform.

Third, setting default streams for new users is a great way to get new users involved in conversations before they've accustomed themselves with joining streams on their own. You can use the set_default_streams command to set default streams for users within a realm:

python manage.py set_default_streams --domain=example.com --streams=foo,bar,...

(3) Notification settings. Zulip gives you a great deal of control over which messages trigger desktop notifications; you can configure these extensively in the /#settings page (get there from the gear menu). If you find the desktop notifications annoying, consider changing the settings to only trigger desktop notifications when you receive a PM or are @-mentioned.

(4) The mobile and desktop apps. Currently, the Zulip Desktop app only supports talking to servers with a properly signed SSL certificate, so you may find that you get a blank screen when you connect to a Zulip server using a self-signed certificate.

The Zulip Android app in the Google Play store doesn't yet support talking to non-zulip.com servers (and the iOS one doesn't support Google auth SSO against non-zulip.com servers; there's a design for how to fix that which wouldn't be a ton of work to implement). If you are interested in helping out with the Zulip mobile apps, shoot an email to zulip-devel@googlegroups.com and the maintainers can guide you on how to help.

For announcements about improvements to the apps, make sure to join the zulip-announce@googlegroups.com list so that you can receive the announcements when these become available.

(5) All the other features: Hotkeys, emoji, search filters, @-mentions, etc. Zulip has lots of great features, make sure your team knows they exist and how to use them effectively.

(6) Enjoy your Zulip installation! If you discover things that you wish had been documented, please contribute documentation suggestions either via a GitHub issue or pull request; we love even small contributions, and we'd love to make the Zulip documentation cover everything anyone might want to know about running Zulip in production.

Maintaining and upgrading Zulip in production

We recommend reading this entire section before doing your first upgrade.

• To upgrade to a new version of the zulip server, download the appropriate release tarball from https://www.zulip.com/dist/releases/ and then run as root:

  /home/zulip/deployments/current/scripts/upgrade-zulip zulip-server-VERSION.tar.gz
  

  The upgrade process will shut down the service, run apt-get upgrade, a puppet apply, and any database migrations, and then bring the service back up. This will result in some brief downtime for the service, which should be under 30 seconds unless there is an expensive transition involved. Unless you have tested the upgrade in advance, we recommend doing upgrades at off hours.

  You can create your own release tarballs from a copy of zulip.git repository using tools/build-release-tarball.

• Warning: If you have modified configuration files installed by Zulip (e.g. the nginx configuration), the Zulip upgrade process will overwrite your configuration when it does the puppet apply. You can test whether this will happen assuming no upstream changes to the configuration using scripts/zulip-puppet-apply (without the -f option), which will do a test puppet run and output and changes it would make. Using this list, you can save a copy of any files that you've modified, do the upgrade, and then restore your configuration. If you need to do this, please report the issue so that we can make the Zulip puppet configuration flexible enough to handle your setup.

• The Zulip upgrade script automatically logs output to /var/log/zulip/upgrade.log; please use those logs to include output that shows all errors in any bug reports.

• The Zulip upgrade process works by creating a new deployment under /home/zulip/deployments/ containing a complete copy of the Zulip server code, and then moving the symlinks at /home/zulip/deployments/current and /root/zulip as part of the upgrade process. This means that if the new version isn't working, you can quickly downgrade to the old version by using /home/zulip/deployments/<date>/scripts/restart-server to return to a previous version that you've deployed (the version is specified via the path to the copy of restart-server you call).

• To update your settings, simply edit /etc/zulip/settings.py and then run /home/zulip/deployments/current/scripts/restart-server to restart the server

• You are responsible for running apt-get upgrade on your system on a regular basis to ensure that it is up to date with the latest security patches.

• To use the Zulip API with your Zulip server, you will need to use the API endpoint of e.g. https://zulip.example.com/api. Our Python API example scripts support this via the --site=https://zulip.example.com argument. The API bindings support it via putting site=https://zulip.example.com in your .zuliprc.

  Every Zulip integration supports this sort of argument (or e.g. a ZULIP_SITE variable in a zuliprc file or the environment), but this is not yet documented for some of the integrations (the included integration documentation on /integrations will properly document how to do this for most integrations). Pull requests welcome to document this for those integrations that don't discuss this!

• Similarly, you will need to instruct your users to specify the URL for your Zulip server when using the Zulip desktop and mobile apps.

• As a measure to mitigate the impact of potential memory leaks in one of the Zulip daemons, the service automatically restarts itself every Sunday early morning. See /etc/cron.d/restart-zulip for the precise configuration.

Backups for Zulip

There are several pieces of data that you might want to back up:

• The postgres database. That you can back up like any postgres database; we have some example tooling for doing that incrementally into S3 using wal-e in puppet/zulip_internal/manifests/postgres_common.pp (that's what we use for zulip.com's database backups). Note that this module isn't part of the Zulip server releases since it's part of the zulip.com configuration (see zulip#293 for a ticket about fixing this to make life easier for running backups).

• Any user-uploaded files. If you're using S3 as storage for file uploads, this is backed up in S3, but if you have instead set LOCAL_UPLOADS_DIR, any files uploaded by users (including avatars) will be stored in that directory and you'll want to back it up.

• Your Zulip configuration including secrets from /etc/zulip/. E.g. if you lose the value of secret_key, all users will need to login again when you setup a replacement server since you won't be able to verify their cookies; if you lose avatar_salt, any user-uploaded avatars will need to be re-uploaded (since avatar filenames are computed using a hash of avatar_salt and user's email), etc.

• The logs under /var/log/zulip can be handy to have backed up, but they do get large on a busy server, and it's definitely lower-priority.

Restoration

To restore from backups, the process is basically the reverse of the above:

• Install new server as normal by downloading a Zulip release tarball and then using scripts/setup/install, you don't need to run the initialize-database second stage which puts default data into the database.

• Unpack to /etc/zulip the settings.py and secrets.conf files from your backups.

• Restore your database from the backup using wal-e; if you ran initialize-database anyway above, you'll want to first scripts/setup/postgres-init-db to drop the initial database first.

• If you're using local file uploads, restore those files to the path specified by settings.LOCAL_UPLOADS_DIR and (if appropriate) any logs.

• Start the server using scripts/restart-server

This restoration process can also be used to migrate a Zulip installation from one server to another.

We recommend running a disaster recovery after you setup backups to confirm that your backups are working; you may also want to monitor that they are up to date using the Nagios plugin at: puppet/zulip_internal/files/nagios_plugins/check_postgres_backup.

Contributions to more fully automate this process or make this section of the guide much more explicit and detailed are very welcome!

Postgres streaming replication

Zulip has database configuration for using Postgres streaming replication; you can see the configuration in these files:

• puppet/zulip_internal/manifests/postgres_slave.pp
• puppet/zulip_internal/manifests/postgres_master.pp
• puppet/zulip_internal/files/postgresql/*

Contribution of a step-by-step guide for setting this up (and moving this configuration to be available in the main puppet/zulip/ tree) would be very welcome!

Monitoring Zulip

The complete Nagios configuration (sans secret keys) used to monitor zulip.com is available under puppet/zulip_internal in the Zulip Git repository (those files are not installed in the release tarballs).

The Nagios plugins used by that configuration are installed automatically by the Zulip installation process in subdirectories under /usr/lib/nagios/plugins/. The following is a summary of the various Nagios plugins included with Zulip and what they check:

Application server and queue worker monitoring:

• check_send_receive_time (sends a test message through the system between two bot users to check that end-to-end message sending works)

• check_rabbitmq_consumers and check_rabbitmq_queues (checks for rabbitmq being down or the queue workers being behind)

• check_queue_worker_errors (checks for errors reported by the queue workers)

• check_worker_memory (monitors for memory leaks in queue workers)

• check_email_deliverer_backlog and check_email_deliverer_process (monitors for whether outgoing emails are being sent)

Database monitoring:

• check_postgres_replication_lag (checks streaming replication is up to date).

• check_postgres (checks the health of the postgres database)

• check_postgres_backup (checks backups are up to date; see above)

• check_fts_update_log (monitors for whether full-text search updates are being processed)

Standard server monitoring:

• check_website_response.sh (standard HTTP check)

• check_debian_packages (checks apt repository is up to date)

If you're using these plugins, bug reports and pull requests to make it easier to monitor Zulip and maintain it in production are encouraged!

Scalability of Zulip

This section attempts to address the considerations involved with running Zulip with a large team (>1000 users).

• We recommend using a remote postgres database for isolation, though it is not required. In the following, we discuss a relatively simple configuration with two types of servers: application servers (running Django, Tornado, RabbitMQ, Redis, Memcached, etc.) and database servers.

• You can scale to a pretty large installation (O(~1000) concurrently active users using it to chat all day) with just a single reasonably large application server (e.g. AWS c3.2xlarge with 8 cores and 16GB of RAM) sitting mostly idle (<10% CPU used and only 4GB of the 16GB RAM actively in use). You can probably get away with half that (e.g. c3.xlarge), but ~8GB of RAM is highly recommended at scale. Beyond a 1000 active users, you will eventually want to increase the memory cap in memcached.conf from the default 512MB to avoid high rates of memcached misses.

• For the database server, we highly recommend SSD disks, and RAM is the primary resource limitation. We have not aggressively tested for the minimum resources required, but 8 cores with 30GB of RAM (e.g. AWS's m3.2xlarge) should suffice; you may be able to get away with less especially on the CPU side. The database load per user is pretty optimized as long as memcached is working correctly. This has not been tested, but from extrapolating the load profile, it should be possible to scale a Zulip installation to 10,000s of active users using a single large database server without doing anything complicated like sharding the database.

• For reasonably high availability, it's easy to run a hot spare application server and a hot spare database (using Postgres streaming replication; see the section on configuring this). Be sure to check out the section on backups if you're hoping to run a spare application server; in particular you probably want to use the S3 backend for storing user-uploaded files and avatars and will want to make sure secrets are available on the hot spare.

• Zulip does not support dividing traffic for a given Zulip realm between multiple application servers. There are two issues: you need to share the memcached/redis/rabbitmq instance (these should can be moved to a network service shared by multiple servers with a bit of configuration) and the Tornado event system for pushing to browsers currently has no mechanism for multiple frontend servers (or event processes) talking to each other. One can probably get a factor of 10 in a single server's scalability by supporting multiple tornado processes on a single server, which is also likely the first part of any project to support exchanging events amongst multiple servers.

Questions, concerns, and bug reports about this area of Zulip are very welcome! This is an area we are hoping to improve.

Security Model

This section attempts to document the Zulip security model. Since this is new documentation, it likely does not cover every issue; if there are details you're curious about, please feel free to ask questions on the Zulip development mailing list (or if you think you've found a security bug, please report it to support@zulip.com so we can do a responsible security announcement).

Secure your Zulip server like your email server

• It's reasonable to think about security for a Zulip server like you do security for a team email server -- only trusted administrators within an organization should have shell access to the server.

  In particular, anyone with root access to a Zulip application server or Zulip database server, or with access to the zulip user on a Zulip application server, has complete control over the Zulip installation and all of its data (so they can read messages, modify history, etc.). It would be difficult or impossible to avoid this, because the server needs access to the data to support features expected of a group chat system like the ability to search the entire message history, and thus someone with control over the server has access to that data as well.

Encryption and Authentication

• Traffic between clients (web, desktop and mobile) and the Zulip is encrypted using HTTPS. By default, all Zulip services talk to each other either via a localhost connection or using an encrypted SSL connection.

• The preferred way to login to Zulip is using an SSO solution like Google Auth, LDAP, or similar. Zulip stores user passwords using the standard PBKDF2 algorithm. Password strength is checked and weak passwords are visually discouraged using the zxcvbn library, but Zulip does not by default have strong requirements on user password strength. Modify static/js/common.js to adjust the password strength requirements (Patches welcome to make controlled by an easy setting!).

• Zulip requires CSRF tokens in all interactions with the web API to prevent CSRF attacks.

Messages and History

• Zulip message content is rendering using a specialized Markdown parser which escapes content to protect against cross-site scripting attacks.

• Zulip supports both public streams and private ("invite-only") streams. Any Zulip user can join any public stream in the realm (and can view the complete message of any public stream history without joining the stream).

• Users who are not members of a private stream cannot read messages on the stream, send messages to the stream, or join the stream, even if they are a Zulip administrator. However, any member of a private stream can invite other users to the stream. When a new user joins a private stream, they can see future messages sent to the stream, but they do not receive access to the stream's message history.

• Zulip supports editing the content or topics of messages that have already been sent (and even updating the topic of messages sent by other users when editing the topic of the overall thread).

  While edited messages are synced immediately to open browser windows, editing messages is not a safe way to redact secret content (e.g. a password) unintentionally shared via Zulip, because other users may have seen and saved the content of the original message (for example, they could have taken a screenshot immediately after you sent the message, or have an API tool recording all messages they receive).

  Zulip stores and sends to clients the content of every historical version of a message, so that future versions of Zulip could support displaying the diffs between previous versions.

Users and Bots

• There are three types of users in a Zulip realm: Administrators, normal users, and bots. Administrators have the ability to deactivate and reactivate other human and bot users, delete streams, add/remove administrator privileges, as well as change configuration for the overall realm (e.g. whether an invitation is required to join the realm). Being a Zulip administrator does not provide the ability to interact with other users' private messages or the messages sent to private streams to which the administrator is not subscribed. However, a Zulip administrator subscribed to a stream can toggle whether that stream is public or private. Also, Zulip realm administrators have administrative access to the API keys of all bots in the realm, so a Zulip administrator may be able to access messages sent to private streams that have bots subscribed, by using the bot's credentials.

  In the future, Zulip's security model may change to allow realm administrators to access private messages (e.g. to support auditing functionality).

• Every Zulip user has an API key, available on the settings page. This API key can be used to do essentially everything the user can do; for that reason, users should keep their API key safe. Users can rotate their own API key if it is accidentally compromised.

• To properly remove a user's access to a Zulip team, it does not suffice to change their password or deactivate their account in the SSO system, since neither of those prevents authenticating with the user's API key or those of bots the user has created. Instead, you should deactivate the user's account in the Zulip administration interface (/#administration); this will automatically also deactivate any bots the user had created.

• The Zulip mobile apps authenticate to the server by sending the user's password and retrieving the user's API key; the apps then use the API key to authenticate all future interactions with the site. Thus, if a user's phone is lost, in addition to changing passwords, you should rotate the user's Zulip API key.

• Zulip bots are used for integrations. A Zulip bot can do everything a normal user in the realm can do including reading other, with a few exceptions (e.g. a bot cannot login to the web application or create other bots). In particular, with the API key for a Zulip bot, one can read any message sent to a public stream in that bot's realm. A likely future feature for Zulip is limited bots that can only send messages.

• Certain Zulip bots can be marked as "API super users"; these special bots have the ability to send messages that appear to have been sent by another user (an important feature for implementing integrations like the Jabber, IRC, and Zephyr mirrors).

User-uploaded content

• Zulip supports user-uploaded files; ideally they should be hosted from a separate domain from the main Zulip server to protect against various same-domain attacks (e.g. zulip-user-content.example.com) using the S3 integration.

  The URLs of user-uploaded files are secret; if you are using the "local file upload" integration, anyone with the URL of an uploaded file can access the file. This means the local uploads integration is vulnerable to a subtle attack where if a user clicks on a link in a secret .PDF or .HTML file that had been uploaded to Zulip, access to the file might be leaked to the other server via the Referrer header (see zulip#320).

  The Zulip S3 file upload integration is relatively safe against that attack, because the URLs of files presented to users don't host the content. Instead, the S3 integration checks the user has a valid Zulip session in the relevant realm, and if so then redirects the browser to a one-time S3 URL that expires a short time later. Keeping the URL secret is still important to avoid other users in the Zulip realm from being able to access the file.

• Zulip supports using the Camo image proxy to proxy content like inline image previews that can be inserted into the Zulip message feed by other users over HTTPS.

• By default, Zulip will provide image previews inline in the body of messages when a message contains a link to an image. You can control this using the INLINE_IMAGE_PREVIEW setting.

Final notes and security response

If you find some aspect of Zulip that seems inconsistent with this security model, please report it to support@zulip.com so that we can investigate and coordinate an appropriate security release if needed.

Zulip security announcements will be sent to zulip-announce@googlegroups.com, so you should subscribe if you are running Zulip in production.

Remote User SSO Authentication

Zulip supports integrating with a corporate Single-Sign-On solution. There are a few ways to do it, but this section documents how to configure Zulip to use an SSO solution that best supports Apache and will set the REMOTE_USER variable:

(0) Check that /etc/zulip/settings.py has zproject.backends.ZulipRemoteUserBackend as the only enabled value in the AUTHENTICATION_BACKENDS list, and that SSO_APPEND_DOMAIN is correct set depending on whether your SSO system uses email addresses or just usernames in REMOTE_USER.

Make sure that you've restarted the Zulip server since making this configuration change.

(1) Edit /etc/zulip/zulip.conf and change the puppet_classes line to read:

puppet_classes = zulip::voyager, zulip::apache_sso

(2) As root, run /home/zulip/deployments/current/scripts/zulip-puppet-apply to install our SSO integration.

(3) To configure our SSO integration, edit /etc/apache2/sites-available/zulip-sso.example and fill in the configuration required for your SSO service to set REMOTE_USER and place your completed configuration file at /etc/apache2/sites-available/zulip-sso

(4) Run a2ensite zulip-sso to enable the Apache integration site.

Now you should be able to visit https://zulip.example.com/ and login via the SSO solution.

Troubleshooting Remote User SSO

This system is a little finicky to networking setup (e.g. common issues have to do with /etc/hosts not mapping settings.EXTERNAL_HOST to the Apache listening on 127.0.0.1/localhost, for example). It can often help while debugging to temporarily change the Apache config in /etc/apache2/sites-available/zulip-sso to listen on all interfaces rather than just 127.0.0.1 as you debug this. It can also be helpful to change /etc/nginx/zulip-include/app.d/external-sso.conf to proxy_pass to a more explicit URL possibly not over HTTPS when debugging. The following log files can be helpful when debugging this setup:

• /var/log/zulip/{errors.log,server.log} (the usual places)
• /var/log/nginx/access.log (nginx access logs)
• /var/log/apache2/zulip_auth_access.log (you may want to change LogLevel to "debug" in the apache config file to make this more verbose)

Here's a summary of how the remote user SSO system works assuming you're using HTTP basic auth; this summary should help with understanding what's going on as you try to debug:

• Since you've configured /etc/zulip/settings.py to only define the zproject.backends.ZulipRemoteUserBackend, zproject/settings.py configures /accounts/login/sso as HOME_NOT_LOGGED_IN, which makes https://zulip.example.com/ aka the homepage for the main Zulip Django app running behind nginx redirect to /accounts/login/sso if you're not logged in.

• nginx proxies requests to /accounts/login/sso/ to an Apache instance listening on localhost:8888 apache via the config in /etc/nginx/zulip-include/app.d/external-sso.conf (using the upstream localhost:8888 defined in /etc/nginx/zulip-include/upstreams).

• The Apache zulip-sso site which you've enabled listens on localhost:8888 and presents the htpasswd dialogue; you provide correct login information and the request reaches a second Zulip Django app instance that is running behind Apache with with REMOTE_USER set. That request is served by zerver.views.remote_user_sso, which just checks the REMOTE_USER variable and either logs in (sets a cookie) or registers the new user (depending whether they have an account).

• After succeeding, that redirects the user back to / on port 443 (hosted by nginx); the main Zulip Django app sees the cookie and proceeds to load the site homepage with them logged in (just as if they'd logged in normally via username/password).

Again, most issues with this setup tend to be subtle issues with the hostname/DNS side of the configuration. Suggestions for how to improve this SSO setup documentation are very welcome!

Postgres database details

Remote Postgres database

This is a bit annoying to setup, but you can configure Zulip to use a dedicated postgres server by setting the REMOTE_POSTGRES_HOST variable in /etc/zulip/settings.py, and configuring Postgres certificate authentication (see http://www.postgresql.org/docs/9.1/static/ssl-tcp.html and http://www.postgresql.org/docs/9.1/static/libpq-ssl.html for documentation on how to set this up and deploy the certificates) to make the DATABASES configuration in zproject/settings.py work (or override that configuration).

If you want to use a remote Postgresql database, you should configure the information about the connection with the server. You need a user called "zulip" in your database server. You can configure these options in /etc/zulip/settings.py:

• REMOTE_POSTGRES_HOST: Name or IP address of the remote host
• REMOTE_POSTGRES_SSLMODE: SSL Mode used to connect to the server, different options you can use are:
  • disable: I don't care about security, and I don't want to pay the overhead of encryption.
  • allow: I don't care about security, but I will pay the overhead of encryption if the server insists on it.
  • prefer: I don't care about encryption, but I wish to pay the overhead of encryption if the server supports it.
  • require: I want my data to be encrypted, and I accept the overhead. I trust that the network will make sure I always connect to the server I want.
  • verify-ca: I want my data encrypted, and I accept the overhead. I want to be sure that I connect to a server that I trust.
  • verify-full: I want my data encrypted, and I accept the overhead. I want to be sure that I connect to a server I trust, and that it's the one I specify.

Then you should specify the password of the user zulip for the database in /etc/zulip/zulip-secrets.conf:

postgres_password = xxxx

Finally, you can stop your database on the Zulip server via:

sudo service postgresql stop
sudo update-rc.d postgresql disable

In future versions of this feature, we'd like to implement and document how to the remote postgres database server itself automatically by using the Zulip install script with a different set of puppet manifests than the all-in-one feature; if you're interested in working on this, post to the Zulip development mailing list and we can give you some tips.

Debugging postgres database issues

When debugging postgres issues, in addition to the standard pg_top tool, often it can be useful to use this query:

SELECT procpid,waiting,query_start,current_query FROM pg_stat_activity ORDER BY procpid;

which shows the currently running backends and their activity. This is similar to the pg_top output, with the added advantage of showing the complete query, which can be valuable in debugging.

To stop a runaway query, you can run SELECT pg_cancel_backend(pid int) or SELECT pg_terminate_backend(pid int) as the 'postgres' user. The former cancels the backend's current query and the latter terminates the backend process. They are implemented by sending SIGINT and SIGTERM to the processes, respectively. We recommend against sending a Postgres process SIGKILL. Doing so will cause the database to kill all current connections, roll back any pending transactions, and enter recovery mode.

Stopping the Zulip postgres database

To start or stop postgres manually, use the pg_ctlcluster command:

pg_ctlcluster 9.1 [--force] main {start|stop|restart|reload}

By default, using stop uses "smart" mode, which waits for all clients to disconnect before shutting down the database. This can take prohibitively long. If you use the --force option with stop, pg_ctlcluster will try to use the "fast" mode for shutting down. "Fast" mode is described by the manpage thusly:

With the --force option the "fast" mode is used which rolls back all active transactions, disconnects clients immediately and thus shuts down cleanly. If that does not work, shutdown is attempted again in "immediate" mode, which can leave the cluster in an inconsistent state and thus will lead to a recovery run at the next start. If this still does not help, the postmaster process is killed. Exits with 0 on success, with 2 if the server is not running, and with 1 on other failure conditions. This mode should only be used when the machine is about to be shut down.

Many database parameters can be adjusted while the database is running. Just modify /etc/postgresql/9.1/main/postgresql.conf and issue a reload. The logs will note the change.

Debugging issues starting postgres

pg_ctlcluster often doesn't give you any information on why the database failed to start. It may tell you to check the logs, but you won't find any information there. pg_ctlcluster runs the following command underneath when it actually goes to start Postgres:

/usr/lib/postgresql/9.1/bin/pg_ctl start -D /var/lib/postgresql/9.1/main -s -o  '-c config_file="/etc/postgresql/9.1/main/postgresql.conf"'

Since pg_ctl doesn't redirect stdout or stderr, running the above can give you better diagnostic information. However, you might want to stop Postgres and restart it using pg_ctlcluster after you've debugged with this approach, since it does bypass some of the work that pg_ctlcluster does.

Postgres Vacuuming alerts

The autovac_freeze postgres alert from check_postgres is particularly important. This alert indicates that the age (in terms of number of transactions) of the oldest transaction id (XID) is getting close to the autovacuum_freeze_max_age setting. When the oldest XID hits that age, Postgres will force a VACUUM operation, which can often lead to sudden downtime until the operation finishes. If it did not do this and the age of the oldest XID reached 2 billion, transaction id wraparound would occur and there would be data loss. To clear the nagios alert, perform a VACUUM in each indicated database as a database superuser (postgres).

See http://www.postgresql.org/docs/9.1/static/routine-vacuuming.html#VACUUM-FOR-WRAPAROUND for more details on postgres vacuuming.