Provide an option to allow custom metrics inside filters.

[chandu188]

The current metrics doesn't provide an option to measure custom metrics inside a filter. We have set of filters which process images (resize, converTojpg) and we would like to measure how long does each step take resize or convertTojpg.

[szuecs]

Do I understand you correctly that you want to know the execution time of a filter? Execution time of a filter would not need to support custom metrics, that's why I ask.

[chandu188]

Sorry if the above description is not clear. Let me try to explain with some examples.

Consider the following as an example of Response method in filter

func ( *articlePath) Response( filters.FilterContext) { step1: convert to jpeg step2: resize image

} currently, the default metrics provide the overall execution time of a filter. It's not possible to measure the execution time of the above 2 steps separately.

Another example could be from this https://github.com/zalando/skipper/blob/8fb107612ac6543f1c76d01bb3e8efe61dac5beb/filters/builtin/compress.go#L367. Here I don't think it's possible to measure the execution time for "encode" method. The default execution time will not be much help for this "compress" filter as it does not measure the time spent in encoding as it runs in a separate goroutine (correct me if I am wrong).

[lmineiro]

This was actually discussed before. There's value on exposing "some" metrics registry to filters We didn't come to a conclusion how to properly namespace that to avoid collisions in the metrics key space.

The suggestion, at the time was:

• Keep the metrics registry protected
• Expose methods to lazily get a metric (timer, counter, etc) under a namespace which should include the filter name
• Serialize filter specific metrics