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gobearmon

gobearmon is a distributed uptime monitoring system.

The basic uptime monitoring concept is simple:

  • Checks, contacts, and alerts are configured in a MySQL database.
  • A check specifies an action verifying that a service is online, e.g. pinging an IP address, opening a TCP connection, or fetching a webpage.
  • A contact specifies a notification action, e.g. sending an e-mail or SMS message.
  • An alert links checks with contacts, e.g. contact Alice and Bob but not Charlie when check X goes offline.

gobearmon is distributed for two reasons. First, to ensure that monitoring continues even if a monitoring node fails. Second, so that notifications are sent only when the check fails on multiple nodes; for example, if a transient network issue interrupts communication between node A and service X, but node B still sees service X is online, then we may not want to send a notification. The distributed system model is:

  • There are N workers and 1 viewserver.
  • At any given time, one worker acts as the controller (master). The viewserver monitors the controller; if the viewserver sees that the former controller is offline, it selects a new controller. Workers query the viewserver to find out who the current controller is.
  • The controller coordinates monitoring among the workers.

Checks

These checks and configuration options are supported:

  • HTTP: can configure timeout, headers, request method/body; can verify the status code or verify that a substring appears in the response body
  • TCP: can configure timeout; can optionally send a payload and verify a newline-terminated response
  • ICMP ping: can configure maximum allowed packet loss out of 5 packets
  • SSL Expiration: can configure the number of days before the certificate expires, e.g. send an alert if the certificate is expired or expiring within 10 days
  • DNS: can configure nameserver, record type, DNS name, and a string that should appear in the DNS response

Monitoring. Each check is configured with an interval and a delay, and there is a global confirmations parameter. The check action is performed every interval seconds. confirmations is how many workers need to agree before flipping the check state (from online to offline or offline to online), and delay is the number of intervals we need to see the new check state before flipping the state. For example, if a check is currently online with interval=60, confirmations=4, and delay=3, then the check is only marked offline if the check action repeatedly fails for 3 minutes, and 4 workers agree that it fails.

Contacts

Contacts can be e-mail, call/SMS via Twilio, or webhook (i.e., perform an HTTP request).

Setup

First, create a MySQL database and initialize tables with install.sql:

$ mysql -u root
> CREATE DATABASE gobearmon;
> use gobearmon;
> source install.sql;

Then, compile gobearmon:

$ go build cmd/gobearmon.go

Configure gobearmon.worker.cfg gobearmon.viewserver.cfg, and copy the compiled gobearmon binary and corresponding configuration file to N workers and 1 viewserver. Run gobearmon:

$ ./gobearmon gobearmon.worker.cfg
or
$ ./gobearmon gobearmon.viewserver.cfg

You can now configure the database. Configuration options are JSON-encoded, see check_params.go for valid options. Add a simple ping check:

INSERT INTO checks (name, type, data) VALUES ('ping ipv6', 'icmp', '{"target":"example.com","force_ip":6}');

Here's a more complex HTTP check, which also sets the check interval/delay:

INSERT INTO checks (name, type, data, check_interval, delay) VALUES ('my http check', 'http', '{"url":"https:\/\/example.com","method":"GET","expect_status":200,"timeout":15}', 120, 5);

Next, add a contact:

INSERT INTO contacts (type, data) VALUES ('email', 'admin@example.com');

Finally, link the check and contact with an alert. For the check type, offline means the contact will only be notified when the check goes offline, online means only when it comes back online, and both means notified in both cases.

INSERT INTO alerts (check_id, contact_id, type) VALUES (1, 1, 'both');

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