I've not heard of anyone making an apache module as yet. right now, linkerd might be the only known reverse proxy that has builtin zipkin support.

We use nginx but same situation, it would be great if we could use trace_ids. Maybe this issue should be moved somewhere else thought as it is not related to the ruby client.

BTW @kmalecki maybe you would be interested on this https://github.com/JordiPolo/lorekeeper
We have a middleware which takes the trace Ids and put it in here so we have nice json formatted log messages with trace_ids. It may be too much depending on how much are you building around querying your logs but it can be a life-saver.

I am also interested in an Apache module to properly start a Zipkin trace. We currently generate Apache spans quite hackily by having Apache log certain Zipkin headers and generating the spans entirely out-of-band. It is very difficult to maintain, though probably has lower in-band overhead.

I think that the only solution is to generate trace id by a module for apache and add header to request. Unfortunately there is no available module, that can generate such thing.
Thank You All for tips.
I will not close this issue yet, maybe I or someone else will find something else.

If it helps anyone, I achieved the above using mod_unique_id and mod_headers:

RequestHeader setifempty X-B3-TraceId "expr=%{md5:%{reqenv:UNIQUE_ID}}"
RequestHeader edit X-B3-TraceId "^(.{0,16}).*$" "$1"

%{reqenv:UNIQUE_ID} is a unique string generated by mod_unique_id. Then, it gets MD5-hashed and assigned to the X-B3-TraceId header. This gives a 32-character hex string = 128 bit traceId. Since my downstream libraries require the traceIds to be 64-bit, the RequestHeader edit extracts the first 16 characters (64 bit) from the value and reassigns it back to the X-B3-TraceId header which is sent downstream.

awesome thanks for sharing @adammichalik!

Does this warrant a small README.md blurb in https://github.com/openzipkin/brave/tree/master/instrumentation/apache-httpd or possibly https://github.com/openzipkin-contrib/apache-httpd ?

maybe in b3 propagation repo, I guess, as it isn't java specific?

@kmalecki were you able to find a working solution for this? I agree with you that if you want a trace span to be generated (and not just propagate the trace context) you probably need a module to handle that.

@sskilbred No, i moved to public cloud and Datadog.

I will close this thread.

Can we reopen this thread? This is a useful feature to have with an Apache DMZ like https://github.com/trajano/docker-oidc-proxy

If it helps anyone, I achieved the above using mod_unique_id and mod_headers:

RequestHeader setifempty X-B3-TraceId "expr=%{md5:%{reqenv:UNIQUE_ID}}"
RequestHeader edit X-B3-TraceId "^(.{0,16}).*$" "$1"

%{reqenv:UNIQUE_ID} is a unique string generated by mod_unique_id. Then, it gets MD5-hashed and assigned to the X-B3-TraceId header. This gives a 32-character hex string = 128 bit traceId. Since my downstream libraries require the traceIds to be 64-bit, the RequestHeader edit extracts the first 16 characters (64 bit) from the value and reassigns it back to the X-B3-TraceId header which is sent downstream.

Hi, really useful thanks. Based on this, I've attempted to do a w3c traceparent header - not sure it is exact as it is intended to be but may be of use. Horribly inefficient though, should really be written as a module!

# Header injection of w3c compliant "traceparent" distributed tracing header
# https://www.w3.org/TR/trace-context/
# This is using mod_unique_id to get uuid for the trace id, and the client ip address as the span/parent id 
# Then use sha1 to convert both to 40 char hex. NB the SHA hashing is not necessary, we just want to hex 
# encode - but haven't come up with any other way to do this using Apache directives. 
# Some concerns around resource utilisation of SHA1 under high volumes, however
# according to https://automationrhapsody.com/md5-sha-1-sha-256-sha-512-speed-performance/ 
# A 2.6Ghz Core i7 can do >1million SHA1 operations/second, so this may not be major concern

RequestHeader setifempty traceparent "expr=%{sha1:%{reqenv:UNIQUE_ID}}-%{sha1:%{REMOTE_ADDR}}" 

# W3C traceparent standard is for a 32 char hex id for trace and 16 char for span, so edit
# accordingly, taking required digits from originally generated, plus add other required elements 

RequestHeader edit traceparent "^(.{32}).*-(.{16}).*$" "00-$1-$2-00"