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Checks and Assets

Checks

Sensu checks are commands executed by the Sensu agent which monitor a condition (e.g. is Nginx running?) or collect measurements (e.g. how much disk space do I have left?). Although the Sensu agent will attempt to execute any command defined for a check, successful processing of check results requires adherence to a simple specification.

Specification

  • Result data is output to STDOUT or STDERR
    • For standard checks this output is typically a human-readable message
    • For metrics checks this output contains the measurements gathered by the check
  • Exit status code indicates state
    • 0 indicates “OK”
    • 1 indicates “WARNING”
    • 2 indicates “CRITICAL”
    • exit status codes other than 0, 1, or 2 indicate an “UNKNOWN” or custom status

Viewing

To view all the checks that are currently configured for the cluster, enter:

sensuctl check list

If you want more details on a check, the info subcommand can help you out.

sensuctl check info my-cool-check

=== marketing-site
Name:           check-http
Interval:       10
Command:        check-http.rb -u https://dean-learner.book
Subscriptions:  web
Handlers:       slack
Runtime Assets: ruby42
Organization:   default
Environment:    default

Management

Checks can be configured both interactively:

create asset

...or by using CLI flags.

sensuctl check create check-disk -c "./check-disk.sh" --handlers slack -i 5 --subscriptions unix
ensuctl check create check-nginx -c "./nginx-status.sh" --handlers pagerduty,slack -i 15 --subscriptions unix,www

To delete an existing check, simply pass the name of the check to the delete command.

sensuctl check delete check-disk

Assets

Assets are a way to provide your checks with runtime dependencies they require to execute. These can be anything from scripts (e.g. check-haproxy.sh) to full runtimes (ruby, python, etc.) Most helpful in environments without a configuration management system, where your systems, images, containers, might not have everything required to run a execute a check.

At runtime the agent sequentially fetches assets and stores them in its local cache. On subsequent check executions it checks for the presence of the asset in its cache and ensures that the contents matches its checksum.

Asset Structure

The agent expects that an asset is a TAR archive that may optionally be GZip'd. Any scripts or executables should be within a bin/ folder within in the archive.

Further when the check is executed, the following are injected into the execution context.

  • {PATH_TO_ASSET}/bin is injected into the PATH environment variable.
  • {PATH_TO_ASSET}/lib is injected into the LD_LIBRARY_PATH environment variable.
  • {PATH_TO_ASSET}/include is injected into the CPATH environment variable.

Storage

At this time the Sensu's backend does not provide any storage capabilities for assets. The assets are expected to be retrieved over HTTP or HTTPS.

Basics

To view all assets currently available in your configured Sensu instance. Run:

sensuctl asset list

If you want more in depth details on an asset, you can use the info subcommand.

sensu asset info my-great-check-sh

Assets can be created both interactively..

create asset

or by using CLI flags.

sensuctl asset create curl --url "https://acme.s3.amazonaws.com/curl-7.52.1.tar" --sha512 d940d3975051f7cb70c28bbf4b45cf4805b5113d44c96ed120e4a8a6206e55ed3fcdabb37158e3989d24267d9e185896e872ab7b10571edc90b62c0a20512346

Filters

Filters are used to specify conditions in-which your asset should be installed on an agent. For example you have a check that's assets have to differ for each platform.

eg.

  • You create an asset name curl/linux; the filter associated with this asset are System.OS=='linux'
  • Next, you create an asset for freebsd named curl/freebsd; the filter would look like System.OS=='freebsd'
  • Finally to associate the assets with a check, you can refer the group by its prefix. Eg. a check named check-website with assets ['curl'].

Sensu Query Language

TODO

Managing Asset Filters

Creating a new asset with filters is as simple as:

sensuctl asset create curl/linux64 --url "http://acme.s3.amazonaws.com/curl-7-linux.tar" --sha512 XXX --filter "System.OS=='linux'" --filter "System.Arch == 'amd64'"

NOTE: At the moment there is no way to edit the filters associated with an existing asset. However, you can re-create the asset with the same name and the existing entity will be overwritten.

To create a new check associated with an asset, run:

sensuctl create check check-my-website --command "curl http://something" --runtime-asset ruby24,python31

Example using the assets prefix:

sensuctl asset create curl/linux --url "http://acme.s3.amazonaws.com/curl-7-linux.tar" --sha512 XXX --filter "System.OS=='linux'" --filter "System.Arch == 'amd64'"
sensuctl asset create curl/macos --url "http://acme.s3.amazonaws.com/curl-7-macos.tar" --sha512 XXX --filter "System.OS=='macos'" --filter "System.Arch == 'amd64'"
sensuctl create check check-my-website --command "curl http://something" --runtime-asset curl # by using prefix captures both assets