Unable to specify Docker host on Windows using named pipes

[godefroi]

I'm using Metricbeat 5.4.2 on Windows Server 2016. I have configured the Docker module as so:

- module: docker
  metricsets:
    - container
  hosts: ["npipe://./pipe/docker_engine"]
  enabled: true
  period: 30s

This configuration passes metricbeat -configtest, but it doesn't actually work. The error message reported in Elasticsearch is this:

Get http://unix.sock/containers/json?: open /pipe/docker_engine: The system cannot find the path specified.

If I use npipe:////./pipe/docker_engine as the host (which matches what I use for Registrator), metricbeat -configtest complains:

PS C:\Program Files\Metricbeat> .\metricbeat.exe -configtest
Exiting: 1 error: host parsing failed for docker-container: error parsing URL: empty host

[godefroi]

It looks to me like the Docker module is using fsouza's go-dockerclient, which is the same client used by Registrator. As Registrator works correctly, this looks to me like it is simply an issue in URI validation. Maybe all that is needed is a special case in ParseURL (beats/metricbeat/mb/parse/url.go) where if the URI starts with npipe:// it just returns the raw string?

[exekias]

I've opened #4751, do you have any way to build and test that branch? Unfortunately, I don't have a Windows scenario to test this fix 😇

[godefroi]

Hm; I built Registrator, it's possible I could work out how to build Metricbeat. Note that it would probably be more correct to use npipe:////./pipe/docker_engine in your tests because that's the URI that go-dockerclient is going to require.

[godefroi]

I put my comments in the PR. I don't know if my simple test is enough to get your PR merged, but it LGTM.

[exekias]

Thanks for the report @godefroi, this fix should make it to next release! (6.0)