Short hostname results in "context deadline exceeded"

[stuart-c]

What did you do?

Added a target with a very short (4 char) hostname and port number combo

What did you expect to see?

Successful polling of the new hostname

What did you see instead? Under which circumstances?

No stats - error of "context deadline exceeded". Still didn't work even if the timeout was increased significantly.

Environment

Official Docker container of Prometheus (:latest)

The following config snippet didn't work:

• job_name: 'jira'
  static_configs:
  • targets: ['jira:8080']

But the following does:

• job_name: 'jira'
  static_configs:
  • targets: ['jirax:8080']

[brian-brazil]

This sounds like a name resolution issue on your end. Have you verified this name resolves and is accessible from within the container?

[stuart-c]

Yep. I used "docker exec" to get into the prometheus container and then could both ping "jira" and telnet to the correct port sending a manual HTTP request and getting the metric data back.

[brian-brazil]

Deadline exceeded implies that DNS worked. Can you access jira via IP address?

Incidentally ping uses non-standard resolution. I wouldn't fully trust it for testing something like this.

[stuart-c]

Yep accessing via IP address works. If I just change the container/link name in Docker to have an extra char it works, so it is just the 4 char hostname/port (jira:8080) which doesn't work. I don't see the callback on the jira exporter side being called at all (this is a Python script using the client library)

[brian-brazil]

Something weird is going on here anyway. Several of my home systems happen to be 4 chars, so I don't think it's on the Prometheus side.

[stuart-c]

Could it be something about being 9 total chars (i.e. host:port = 4:4 chars)?

It was a very odd thing and as I say just changing the hostname fixed it

[brian-brazil]

This is likely something odd with resolution on your end. If this is still occurring, it's best to discuss on https://groups.google.com/forum/#!forum/prometheus-users

[lock]

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