Discovering dynamic port assignment

Elastic Stack Elasticsearch
1

Is there a method by which you can easily / programmatically obtain the HTTP / Transport port number when starting a node using the -Ehttp.port=0 or -Etransport.tcp.port=0 arguments?

Specifically, i'm bringing up an ES node as part of an integration test, which will eventually run on a CI server. As multiple jobs may run concurrently, I need to avoid hard coding the ports numbers when bringing up the node. I can use the above arguments (or a range) to ensure that if there is a port conflict with an already running process, the node will still come up on another port - but short of parsing the elasticsearch.log file (or inspecting the output of a command like netstat for the node pid), is there a way to obtain the ports used.

For example, you can use the -p option to save off the PID to a file, but there isn't a similar (documented) option for ports.

(Yes Docker would be one solution, but not what i'm looking for comment on here)

2

You can not run elasticsearch embedded. Read this blog post.

Note that to run integration tests (not unit tests) you would probably prefer running that in something close to a production environment, like a real elasticsearch server instance. I shared some ideas about integration testing in this thread: In memory testing with RestHighLevelClient

3

David, I'm not trying to run it embedded, i am starting a node as its own process with the -Ehttp.port=0 cli argument to bin/elasticseach, which will start the http service on a random unassigned port. what i need is a way to discover that port assignment for use with the high-level rest client.

As noted, i could log scrap to get it but I was hoping for a better method.

4

I see. I was unsure with that:

i'm bringing up an ES node as part of an integration test

TBH I was not aware that you can start a node with -Ehttp.port=0 or -Etransport.tcp.port=0.

As noted, i could log scrap to get it but I was hoping for a better method.

I guess that's the only method for now. Wondering if this is something that would deserve a feature request... First time I'm seeing that need TBH so I'm unsure about what the team will say.

@rjernst WDYT?

5

Using port 0 just means find a free port: ServerSocket(0):

port - the port number, or 0 to use a port number that is automatically allocated.

Are there any JMX metrics exposed that might be useful here, for connection via JMX Local Monitoring?

6

I don't think there is anything like that.

7

Well in the hope this can be actioned:

8

This is what we do in tests. It means to use an ephemeral port.

9

I naively thought it was something set by gradle (like a random port with a check that nothing is running). :grin:

10

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