Using environment variable for square brackets is not documented, not obvious

[matthughes]

The example config in elasticsearch.yml is:

#discovery.zen.ping.unicast.hosts: ["host1", "host2:port"]

Using environment variables, I would assume to replace everything in square brackets:
export ES_HOSTS="[host1, host2:port]" discovery.zen.ping.unicast.hosts: $ES_HOSTS

This does not parse correctly though. The only way I could get it to work was omit the brackets:
export ES_HOSTS="host1, host2:port" discovery.zen.ping.unicast.hosts: $ES_HOSTS

Given that this is not documented, not obvious, and also parses fine as:
#discovery.zen.ping.unicast.hosts: "host1", "host2:port"

I propose we change the default config file. There is also no other use of square brackets in the config file.

[matthughes]

https://groups.google.com/forum/#!topic/elasticsearch/RlyeFhnZjlI

[clintongormley]

Hi @matthughes

Sorry it has taken a while to look at this. The config file is just YAML, and arrays are perfectly acceptable in YAML, so I don't think it is worth preventing arrays from working.

I agree though that the documentation could be improved, specifically here: http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/setup-configuration.html#styles

[debadair]

The relevant topic is now at: https://www.elastic.co/guide/en/elasticsearch/reference/current/settings.html

[elasticmachine]

Pinging @elastic/es-core-infra

[rajat-garg]

Hey, I want to pick this up as my first OS contribution. Can someone help me?

[debadair]

[docs issue triage]

[lockewritesdocs]

Looking at the Configuring Elasticsearch page for 7.6, there are no brackets included in examples. The only inclusions of brackets in a supported version are in the 6.8 version, which shows:

Enter value for [node.name]:

@debadair, is that a worthwhile change? Otherwise, it seems this issue is no longer relevant.

[lockewritesdocs]

Talked to @jrodewig about this one, and he thinks that there's value in documenting how arrays work for environment variables.

[lockewritesdocs]

I did some limited testing with the following variables in elasticsearch.yml:

node.name: ${HOSTNAME}
discovery.seed_hosts: ${HOST1}, ${HOST2}

If I include brackets around the variables [] like in an array, Elasticsearch throws an error and fails to start. Entering the variables without the brackets (as shown), I then ran:

export HOST1="127.0.0.1"
export HOST2="127.0.0.1:12"
export HOSTNAME="valhalla"

I then started Elasticsearch, which started normally. My takeaway is that brackets are not required when passing multiple variables in elasticsearch.yml. I think that we can enhance the examples in the Environment variable substitution section to show multiple variables and indicate that brackets are not required.

@rjernst, can you please review my findings and let me know if I'm on the right track? I'm still learning who does what, but I think that this is your area of expertise.