Add support for Redis unix sockets

[brennentsmith]

Adds support for unix sockets on connecting to redis. Can result in a 50% increase in performance (https://redis.io/topics/benchmarks) and provides a touch of local ACL’s (permissions on the local file descriptor).

We use Redis heavily at Speedtest.net as a local pre-buffer for logstash, and using unix sockets helps reduce the local overhead.

Corresponding logstash-output-redis PR: logstash-plugins/logstash-output-redis#57

[brennentsmith]

Signed CLA. Rebuild

[jordansissel]

Change looks pretty straight-forward.

I'd like to see mutual exclusion on path vs host and port -- if a user specifies both path and host, Logstash should fail.

[jordansissel]

I'll test this (and your other PR on redis output) tomorrow. Thank you for your work :)

[brennentsmith]

👍 Sounds good on the mutual exclusion - PR updated.

[brennentsmith]

Rebuild. Travis seemed to have a networking issue.

[jordansissel]

I restarted the failed redis job. (3/4 passed, 1 failed due to network issues)

[jstoja]

This is probably mergeable! :)

[jsvd]

to reduce a minor breaking change subtlety in treating the default parameters I think we should keep the default value for host in the setting itself but make :path override it if set (and log a warn).

[jsvd]

I think we can keep this default here, and simple have the :path option overwrite host/port like described in line 34

[jsvd]

If :path is set we can just log a warn saying that path is set, so we're ignoring host/port

[brennentsmith]

Thanks @jsvd for the feedback. Ironically, that was actually the original logic of how this PR was constructed (see commit: 7c29668) Looks like I forgot to remove the comment on L34 in the subsequent commits 😆 .

@jordansissel - thoughts? I can see merits for both logic paths:

1. Mutually exclusive

• No ambiguity about which connection is being used
• Defaults are no longer set at init, which does make the code more complex

2. Override

• Could potentially lead to confusion (especially if someone doesn't know what unix sockets are). Documentation can help assay this issue, but it's not as explicit as a mutex.
• Defaults are set at init, making the code cleaner.

Frankly, I'm fine with either logic path - just let me know which pattern matches Logstash plugins best and I'll update the PR.

[jsvd]

@brennentsmith thank you for the contribution, this is great!

[brennentsmith]

@jsvd - logic updated as requested.

[jsvd]

LGTM