SUSE Manager/SaltTimeoutsForMinions

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A quick introduction to Salt timeouts

Salt features two timeout parameters called timeout and gather_job_timeout that are relevant during the execution of Salt commands and jobs--it does not matter whether they are triggered using CLI or API. These two parameters are explained in the following article.

This is a normal workflow when all minions are well reachable:

  1. A salt command or job is executed: salt '*'
  2. Salt master publishes the job with the targeted minions into the Salt PUB channel.
  3. Minions take that job and start working on it.
  4. Salt master is looking at the Salt RET channel to gather responses from the minions.
  5. If Salt master gets all responses from targeted minions, then everything is completed and Salt master will return a response containing all the minion responses.

If some of the minions are down during this process, the workflow continues as follows:

  1. If timeout is reached before getting all expected responses from the minions, then Salt master would trigger another job (a Salt find_job job) targeting only pending minions to check whether the job is already running on the minion.
  2. Now gather_job_timeout is evaluated. A new counter is now triggered.
  3. If this new find_job job responses that the original job is actually running on the minion, then Salt master will wait for that minion's response.
  4. In case of reaching gather_job_timeout without having any response from the minion (neither for the initial nor for the find_job job), Salt master will return with only the gathered responses from the responding minions.

By default, SUMA globally sets timeout and gather_job_timeout to 120 seconds. So, in the worst case, a Salt call targeting unreachable minions will end up with 240 seconds of waiting until getting a response.

Synchronous calls with unreachable Salt minions: a presence ping mechanism

In order to prevent waiting until timeouts are reached when some minions are down, SUSE introduced a so-called "presence mechanism" for Salt minions.

On SUMA 3.0.5 and later, this presence mechanism checks for unreachable Salt minions when SUMA is performing synchronous calls to these minions, and it excludes unreachable minions from that call. Synchronous calls are going to be displaced in favor of asynchronous calls but currently still being used during some workflows.

The newly introduced presence mechanism triggers a Salt with a custom and fixed short Salt timeout values. Default Salt values for the presence ping are: timeout = 4 and gather_job_timeout = 1. This way, we can quickly detect which targeted minions are unreachable, and then exclude them from the synchronous call.

Overriding Salt presence timeout values (/etc/rhn/rhn.conf)

SUMA administrators can increase or decrease default presence ping timeout values by removing the comment markers (#) and setting the desired values for salt_presence_ping_timeout and salt_presence_ping_gather_job_timeout options in /etc/rhn/rhn.conf:

   # SUSE Manager presence timeouts for Salt minions
   # salt_presence_ping_timeout = 4
   # salt_presence_ping_gather_job_timeout = 1

Salt SSH Minions (SSH Push)

Salt SSH minions are slightly different that regular minions (zeromq). Salt SSH minions do not use Salt PUB/RET channels but a wrapper Salt command inside of an SSH call. Salt timeout and gather_job_timeout are not playing a role here.

SUMA defines a timeout for SSH connections in /etc/rhn/rhn.conf:

  # salt_ssh_connect_timeout = 180

The presence ping mechanism is also working with SSH minions. In this case, SUMA will use salt_presence_ping_timeout to override the default timeout value for SSH connections.