How to plan maintenance windows using silencing

What is Sensu silencing?

As check results are processed by a Sensu backend, the server executes event handlers to send alerts to personnel or otherwise relay event data to external services. Sensu’s built-in silencing, along with the built-in not_silenced filter, provides the means to suppress execution of event handlers on an ad hoc basis.

When to use silencing

Silencing is used to prevent handlers configured with the not_silenced filter from being triggered based on the check name present in a check result or the subscriptions associated with the entity that published the check result. This can be desirable in many scenarios, giving operators the ability to quiet incoming alerts while coordinating their response.

Sensu silences make it possible to:

Using silencing to plan maintenance

The purpose of this guide is to help you plan a maintenance window, by creating a silenced entry for a specific entity named i-424242 and its check named check-http, in order to prevent alerts as you restart or redeploy the services associated with this entity.

Creating the silenced entry

The first step is to create a silenced entry that will silence the check check-http on an entity named i-424242, for a planned maintenance window that starts at 01:00, on Sunday, and ends 1 hour later. Your username will automatically be added as the creator of the silenced entry.

sensuctl silenced create \
--subscription 'entity:i-424242' \
--check 'check-http' \
--begin '2018-03-16 01:00:00 -04:00' \
--expire 3600 \
--reason 'Server upgrade'

See the sensuctl documentation for the supported time formats in the begin flag.

Validating the silenced entry

You can verify that the silenced entry against our entity, here named i-424242, has been properly created, by using sensuctl.

sensuctl silenced info 'entity:i-424242:check-http'

Once the silenced entry starts to take effect, events that are silenced will be marked as so in sensuctl events.

sensuctl event list

   Entity         Check        Output       Status     Silenced          Timestamp
──────────────   ─────────    ─────────   ──────────── ────────── ───────────────────────────────
   i-424242      check-http                    0          true     2018-03-16 13:22:16 -0400 EDT

WARNING: By default, a silenced event will be handled unless the handler uses the not_silenced filter to discard silenced events.

Next steps

You now know how to create silenced entries to plan a maintenance and hopefully avoid false positive. From this point, here are some recommended resources: