Snap! C++ is a website backend project mainly written in C++ (there is a little bit of C and it uses many C libraries...)
The project includes many libraries, many daemons/servers, it supports plugins for third party extensions, and it uses Cassandra as its database of choice (especially, a NoSQL, although Cassandra now has CQL...)
Click on this link to go to the official home page for the development of Snap! C++. The website includes documentation about the core plugins and their more or less current status. It also includes many pages about the entire environment. How things work, etc.
Each project has an Open Source license, however, it changes slightly depending on the project. Most of the projects use the GNU GPL or GNU LGPL version 2. You will also find public domain code and MIT or FreeBSD licenses.
Details About Snap! Websites
Please make sure to understand that Snap! Websites are not for a one quick computer install a la Wordpress or Drupal. Snap! Websites only runs well on a cluster. It is built to run any number of websites within one cluster. Making it easy to share resources of large powerful websites with tiny websites. Both benefit from the other!
Your cluster should have at least:
- 4 frontend computers to run Apache2,
- 4 Cassandra nodes (at least 2 CPU and 4Gb of RAM)
- 1 snapbackend computer (for the CRON like tasks) (1Gb)
- 1 other services (mail, DNS, etc.) (1Gb)
Less than those 10 computers and you are likely to have some slowness unless you have a monster computer with 14 processors, really fast hard drives (i.e. SSD), and a lot of RAM (32Gb+). But even that won't work right because you want separate computers for the Cassandra nodes. Otherwise loss of data is very high (only the Cassandra cluster retains website data, other computers may have various caches, but they do not retain the official website data.)
The reason for having at least 4 Cassandra nodes is because you want a minimum of 3 as the replication factor and with only 3 computers, you cannot do an upgrade without stopping everything. With 4 computers, you can stop one Cassandra node, upgrade that computer, restart the node. Proceed to the next node.
Note: ScyllaDB should work just fine too. We are planning in testing that theory soon.
Note that the number of frontend computers, middle-end if you separate
snapserver entries, and the Cassandra nodes can be much larger.
At this time we think that the current implementation can support up
to 300 computers in all, without too much trouble. In other words,
the system is built to grow horizontally. If all your Cassandra nodes
are always very busy (75%+) or all your frontend computers are always
very busy, then you can just add more and the load will automatically
be shared between the additional computers. (It is not currently
dynamic, but we may at some point offer such a capability too!)
Backend Growth, also horizontal
Similarly, some of the backends can be duplicated to share the load, although there are some limits on this one: one backend process can run against one website; another backend instance on another computer can run against another website. So in other words, we do not allow multiple backend run against the same website in parallel.
Developement and Testing
To test or as a developer, you can test on a single machine, but of course that won't prove the cluster mechanisms work as expected. For such a test, you should at least have 8Gb or have another machine to run a Cassandra node.
In other words, you do not need to have a cluster to work on Snap! Websites as a developer. You can even have a single Cassandra node. It will be somewhat slower, but it is bearable. Of course, as a developer with a single node, you may lose the data in that node, but I would imagine it would only be test data...
A Snap! Websites Cluster
The following images shows you an installation example. The cloud represents
clients accessing your Snap! environment. The
Apache + snap.cgi represents
access points (you can have as many as you want to load balance the incoming
hits). All the other computers can be 100% private (i.e. no direct access to
the Internet). The
snapserver computers represent the frontend of Snap!
(middle-end as far as the cluster is concerned.) At some point
will be smart enough to auto-load balance your stack, right now we just use
a simple round robin DNS definition. The Cassandra computers each run one
node. Those must have at least 4Gb of RAM in a valid live system. The
snapbackend run CRON like tasks. However, those are dynamic and receive a
PING message from the
snapserver whenever a client makes a change (on a
POST). So really it does work in the background but instantly once data to
crunch is available.
The Snap! Websites Stack
another picture and more details on this page
showing how the processes are linked together. It does not show all
the details, such as the fact that
snapcommunicator is used as the
inter-process and inter-computer hub (i.e.
snapserver sends the
PING message to
snapcommunicator, which knows where the
are and thus forwards the message to the correct computer automatically.)
We see that a connection has to first be accepted by the firewall which
is dynamically updated by our anti-hacker/spam processes. If it does go
through, it gets sent to Apache2. If Apache2 is happy (you may put all sorts
of protections in Apache2 such as
mod_security), then it loads
and runs it with a set of variables representing the header we just
received and a packet with POST data if any was attached.
At that point, the
snap.cgi choose a
snapserver that's not too loaded, and
sends the access data to it and wait for the reply which is then sent to
Apache2 and finally back to the client.
snapserver will access the database, Cassandra, through the
snapdbproxy daemon (which allows us to have the system go really fast
because we connect to it on localhost instead of directly to Cassandra,
which can be much slower, especially if through an SSL connection. We also
gather the meta data only once and cache it.)
If you are an administrator who just wants to install Snap! on your systems, then you want to look at the Launchpad section below.
If you are a developer and want to work on the source code, check We are using the PPA environment again at this time... If you want a pre-compiled version, that's the way to go!
Basics about the Snap! C++ Projects
We now make use of Launchpad, also called the PPA repository of Ubuntu, to compile and generate all our public Snap! packages.
We currently have three main sections:
- contribs, and
The cmake folder includes various cmake scripts used to handle the Snap! C++ development environment.
The contribs are independent libraries, many of which we authored especially for Snap! C++ but that can be used in other projects with very minor help. A couple (log4cplus and zipios) are actually third party libraries which we compile specifically because Ubuntu does not offer that latest greatest version yet. We intend to stop supporting those on the edge versions once we can switch to the latest version available as is in the Ubuntu repository.
The snapwebsites project is the Snap! C++ environment. Although it is composed of many sub-projects, these would be difficult to use on their own. We still have one or more packages per project. Often we break down a project by library, tools, development, and documentation. Along the way, we break-up various parts as contrib libraries instead (for example, the libaddr and libexcept constribs are two libraries that were created from the libsnapwebsites code that we wanted to reuse in other contribs.)
Getting Packages from Launchpad
We offer a PPA with all the projects found in Snap! C++.
To get that to work on your system, you want to install the PPA in your apt-get environment. The following are the two lines you can add to your apt-get source files to make things work.
deb http://ppa.launchpad.net/snapcpp/ppa/ubuntu xenial main deb-src http://ppa.launchpad.net/snapcpp/ppa/ubuntu xenial main
You can also use the
apt-add-repository command as follow:
sudo apt-add-repository ppa:snapcpp/ppa
This way, you automatically get the keys installed so you don't have to do that manually.
Once you've upgraded the PPA, you can see a new file under
/etc/apt/sources/list.d. It should be named something like this:
If you had other snapcpp list files, you probably want to remove them.
TODO: We currently don't offer the Cassandra C++ Driver as a third party was offering it. We are now thinking it would be easier for us to include another contrib entry with that driver so it works with whatever version of Ubuntu we want to support.
The first installation requires the snapmanagercgi package:
sudo apt-get update sudo apt-get install snapmanagercgi
The computer after that command should be ready to accept your installations
snapmanager.cgi browser interface, although you may need to tweak
a few things to get Apache and
snapmanager.cgi to work together. It works
as is for us on DigitalOcean and our VPS using VirtualBox on our development
To upgrade later, run an
does it for you, but if you like to see the output, that's the easiest way,
snapmanager.cgi it runs an upgrade on all your
computers at once:
sudo apt-get update sudo apt-get dist-upgrade
Note that the Upgrade in the
snapmanager.cgi interface works the same
way as these last two commands. So if you add the Snap! C++ repository to
all your nodes you can then use the
snapmanager.cgi interface to run an
upgrade on your entire cluster.
Once ready, the
snapmanager.cgi gives you access to a list of bundles.
These are used to install a part to your system. For example, the Cassandra
nodes don't get the
snapbackend bundle installed. However, attempting to
install Snap! C++ by hand is complicated. There are small setups to do which
if you miss them prevents the system from working correctly. I'm the author
and frankly, there are just way too many things to remember about to not be
snapmanager.cgi to proceed with installations.
Installing a Website
Once you installed the
snapserver bundle, you may start installing a
website. At the moment this is complicated because we do not have a
snapmanager.cgi interface quite yet. You may use the GUI, but when
installing a remote version of Snap! C++, it's complicated (as it requires
an ssh tunnel.)
First we want to prepare the database context. Note that this may take a little time as the process waits for the creation to be complete before returning.
Right now, the snapdbproxy won't detect that the new context was created. It needs to be restarted so we can create the tables:
sudo systemctl restart snapdbproxy
At some point we are thinking to get the
snapdbproxy to do the work
of creating the context and tables. Then later to understand requests
to install a new website in the database. That way, you won't have to
worry about having to do that yourself. The
snapdbproxy can easily
detect whether the context exists and check the tables before accepting
connections from other parts of the system.
Next we want to install the tables in the context. The tables are declared in XML files so the tool can read those and do the necessary work.
Tables are assigned a name and a model. The model defines many parameters so Cassandra has a better chance to handle that table properly.
Once the tables were created, it is possible to install the domain name,
website name, and then the actual website data. This is currently all
done in one go with the
snapinstallwebsite tool, although with that
tool we currently limit the installation to a standard/default setup.
Later it will be possible to edit or provide more advanced declarations
for your domains and websites so you can manage much more complex
parameter gathering from your domain name and website path.
snapinstallwebsite --protocol HTTP --domain www.snap.website --port 80
At this time we support port 80 and 443.
The domain name may or may not include a sub-domain name.
The installation of the domain and website is extremely fast (very small parameters to save to the database.) What followe, however, requires more time.
By default, the tool is verbose and informs you of the current step in the installation process. The last step says:
Status: Initialization succeeded.
Unless you encounter a problem while initializing. You may re-run the process multiple times until you get a postive outcome. However, some errors won't be corrected with additional run. They will instead have been skipped.
Now the first website is ready for viewing in your browser. You should be able to visit the front page with:
The information may not be available to the existing instance. To make sure that the newest everything (tables, data, etc.) is ready for use, you may want to reboot your cluster once. This will reset all memory caches and make sure all the daemons are running as expected. Then try again to access your website.
From Sources (For Advanced Developers)
I suggest you first run bin/snap-ubuntu-packages to get all
dependencies installed. Then do
The whole environment is based on
cmake and also matches
pbuilder so we
can create Ubuntu packages with ease (
cmake even makes use of the control
files to generate the inter project dependencies!) We do not yet release
the Ubuntu packages publicly. We have a launchpad.net environment, but
unfortunately, it is too complicated to use when you manage a large
project that includes many sub-projects.
To compile everything you have one dependency on the C++ Cassandra Driver. This can be obtained from the following PPA:
sudo add-apt-repository ppa:tcpcloud/extra sudo apt-get update sudo apt-get install cassandra-cpp-driver-dev
To get started quickly, create a directory, clone the source, then run the build-snap script. (You may want to check it out once first to make sure it is satisfactory to you.) By default it build snaps in Debug mode.
snap-ubuntu-packages installs many packages that the build
requires. This is done automatically in the build system using the control
file information. For a developer, that's not automatic. So the easiest
is to run that command. Although we try to keep it up to date, if something
cmake should tell you. Worst case scenario, the compiler stops
with an error. We recommend the --optional packages so you get full
documentation and some extras for tests.
apt-get install git mkdir snapwebsites cd snapwebsites git clone --recursive https://github.com/m2osw/snapcpp.git snapcpp snapcpp/bin/snap-ubuntu-packages --optional snapcpp/bin/snap-build
For a clone that ends up being a read/write version, then you want to use a slightly different URL for the purpose:
git clone --recursive email@example.com:m2osw/snapcpp.git snapcpp
After a while, you'll have all the built objects under a BUILD directory
snapwebsites directory. The distribution being under the BUILD/dist
directory (warning: executables under the distribution will be stripped
RPATH which means you cannot run them without some magic;
namely changing your
We support a few variables, although in most cases you will not have to setup anything to get started. You can find the main variables in our bin/build-snap script which you can use to create a developer environment. There is an example of what you can do to generate the build environment. The build type can either be Debug or Release.
cmake \ -DCMAKE_BUILD_TYPE=Release \ -DSNAP_COMMON_DIR:PATH="`pwd`/BUILD/dist/share/snapwebsites" \ ..
Building Launchpad Packages
To rebuild all the packages on Launchpad, we have all the necessary scripts in our makefiles. Once you ran cmake successfully, say under a directory named BUILD, then you can run the following command:
make -C BUILD dput
This will prepare all the source packages and upload them to the Launchpad repository. The files are not going to be uploaded if their version did not change. To change the version of a project, edit its changelog file and add an entry at the beginning of the file. In most cases this is about what changed in your last commit(s). If you did not really change anything but still need a rebuild (i.e. a dependency changed but the PPA was not smart enough to rebuild another package.) then increase the 4th number and put a comment about the fact this is just to kickstart a build of that project.
Making sure packages will build on Launchpad
Whenever you are ready to build on the PPA, you may want to first check
whether everything builds on your system. If you used the snap-build scripts,
you have two folders:
BUILD folder is generally
the one you use on your development system since it's the debug version. That
also means the
RELEASE rarely gets rebuilt. This is where a Launchpad
compilation happens, though, and therefore not having that rebuild on your
system would show you that the PPA is going to have a problem on its own.
So, we suggest that you run a
RELEASE build once before attempting a PPA
build with the following command:
make -C RELEASE
If that fails, then the PPA will sure fail. Make sure you have the latest version of everything, check where the error occurs, try compiling and fixing just that one project until it works, and push all your changes if any, then run the PPA update.
Setting up a development environment
TODO: need to complete this one...
Once you compiled everything, you will have an environment that can be
used to run Snap! Only, it won't work as is. You first have to setup a
certain number of parts:
/var/cache/snapwebsites, and make sure
snapmanagerdaemon starts as root.
Although these things do get installed automatically when you install
the Snap! packages, doing so with the packages will install these files
snapwebsites:snapwebsites (user/group) and that is not practical
when trying to debug Snap!, since you'll want to quickly edit these
To build Ubuntu packages, you want to run the following commands, although this is currently incomplete! We will try to ameliorate that info with time. It currently takes 1h30 to rebuild everything as packages. (Note that it can be parallelized and run a lot faster that way, like 10 to 15 minutes.)
# get some extra development tools if you don't have them yet apt-get install ubuntu-dev-tools eatmydata debhelper # create the build environment (a chroot env.) pbuilder-dist `lsb_release --codename --short` create # Prepare source packages make debuild # Create packges make pbuilder
At this point we only have a Linux version of the project. We have no plans in updating the project to work on a different platform, although changes are welcome if you would like to do so. However, as it stands, the project is not yet considered complete, so it would be quite premature to attempt to convert it.
Note that the software makes heavy use of the
fork() instruction. That
means it will be prohibitive to use under earlier versions of MS-Windows
(i.e. MS-Windows 10 and newer offer the
fork() instruction now.)
Submit bug reports and patches on github.
This file is part of the snapcpp project.