Apply changes from configuration file without restarting

[suyograo]

Today, any config changes made to LS pipeline requires a process restart, which is not ideal. Plan is to implement a feature which would track config file for changes and restart the pipeline (same process) with updated changes. This feature can be enabled in two ways:

1. Passing a CLI long-form option --auto-reload or with short-form -r. Another option: --reload-interval <seconds> controls how often LS should check the config files for changes.
2. If you don't start with the CLI option, you can send SIGHUP or kill -1 to signal to LS to reload the config file and restart the pipeline.

bin/logstash -f apache.config --auto-reload

Behaviour:

When Logstash detects a change in config, it stops the current pipeline by stopping all the inputs, and attempts to creates a new pipeline using the updated config. A configuration test is run on the new configuration to make sure everything is good syntax wise. Then a new pipeline is created if there are no errors -- all inputs and outputs can be initialized (e.g. ports open). Once successful, the existing pipeline is swapped with the new pipeline. If there are errors, the old pipeline continues to function as before, and the errors are propagated to the console.

When a config is reloaded, the JVM is not restarted. All of this is in-process

Note that --auto-reload is not available with -e flag which lets users pass in configuration through the CLI.

[djschny]

For service oriented apps I wrote in the past that had this behavior, I expanded to include the refreshing from any URL, that way one easy way to get centralized config management was via a web server or similar. For example:

• file://
• http://
• https://
• ftp://

If you're in Java land, accomplishing this is pretty easy too using something similar to new URL("<my_config_url>").openStream() and regardless of what protocol you're given a stream to read from.

[jsvd]

@djschny we support the same in logstash through open-uri https://github.com/elastic/logstash/pull/4520/files#diff-5e1ebf137d1eab8a085fa7c1c4a6fd2cR37
However we're restricting to http/https and file (for no go reason).

[jsvd]

merged in master:

Branch	Commits
master	a90ed32, e38d815, 34ed3c3, 7ee5038, e32f732, 7d8d6e4

I'll open a new PR to add this to 2.x since the branches have greatly diverged

[suyograo]

@jsvd great stuff, keeping this open until its backported to 2.x

[lawre]

How does the dynamic reload work with systemd service? I perused /etc/sysconfig/logstash and saw no variables corresponding to 'auto_reload' or 'reload_interval'

[jsvd]

in #LS_OPTS="" you can set LS_OPTS="-r" to have auto reloading

[jsvd]

merged in 2.x

Branch	Commits
2.x	0099537