Adding extra fields to access logging

[neoreddog]

Problem:

Observing network traffic with Linkerd is a step-backwards from Istio as fields like ‘x-forwarded-from’ are missing from the access logs. This makes it difficult to identify where a request comes from.

As partly described in Issue #9842 linkerd/linkerd2#9842.

Access logs also lack a path and query field and instead provide only the entire uri, again a QOL problem that makes it harder to adopt Linkerd.

Solution:

Adding in three fields,

x_forwarded_for
requested_server_name
path

The first two fields are extracted from the request headers using the pre-existing get-header method.

The path field is extracted from the request.uri().path_and_query() method and defaults to "" if no path can be extracted from the uri.

Validation:

Building and deploying the customised linkerd proxy with access logs enabled alongside a nginx container.

Sending network requests and validating that all pre-existing fields persist and the new ones function as intended.

Fixes:

Part fixes #9842

I agree to the DCO for all the commits in this PR.

[neoreddog]

While working I don't think the current implementation is ideal. Hardcoding the x-envoy-decorator-operation header is only applicable when using an envoy proxy and isn't part of an RFC.

I'd like to work on this more and look at adding runtime args or a configuration option to include custom headers, then it'd be more useful to the community as a whole.

Is there a preference for any specific method?

• Runtime args
• Env var
• Config option