Why not use the requestid URL parameter for your requests, which is already included in api.log?

Or if you're talking about logging in general, @bd808 might be able to tell us of a way to get it added to all log messages that go into logstash. Possibly WikiProcessor.php, if I had to guess, or a new processor added to the list in $wgMWLoggerDefaultSpi.

In T97226#1236309, @Anomie wrote:

Or if you're talking about logging in general, @bd808 might be able to tell us of a way to get it added to all log messages that go into logstash. Possibly WikiProcessor.php, if I had to guess, or a new processor added to the list in $wgMWLoggerDefaultSpi.

The current Monolog config for production is using Monolog's UidProcessor to add a correlating id to all log messages for a given PHP request. The right thing to do would probably be to create a new subclass of UidProcessor that looks for the X-Request-ID header and uses its value when found instead.

To make propagating an X-Request-ID among layers easier we should introduce some easy way to get the value that also transparently generates and remembers a conforming value if none in present for the current request. This could then be wired into not only the logging layer but also used to decorate all outbound curl requests.