Re: Allow gorouter to log random headers.

Gwenn Etourneau

So if you move to Heroku you will be able to change the platform ??? I
don't think so..
So you can put the new header from your app or at least the runtime
buildpack or docker.

Your application should be platform dependent that's why you need to
implement this header into your application to avoid any lock-in or forking

On Wed, Jul 22, 2015 at 6:27 PM, Simon Johansson <simon(a)>

WAKAWAKA is just an example
But the difference is that WAKAWAKA is not platform specific whereas
X-Cf-Requestid is. If we want to move our app to Heroku, or a VM, or
whatewher we have platform specific implementation details in our
app(namely we rely on a header that is not there anymore). But that is not
the point of this thread.

The point is,

say we have an app that is fronted by a CDN, and the CDN sets the
X-Im-a-shark header with some value that we are interested to see in our
logs. The easiest way to achivie this without having to implement it into
our own apps is just to tell the Gorouter that it should append the value
of that header into the string that it logs so the event that flow via
Doppler and ultimately into cf logs/ELK will contain that value.

The reason why this would be such a valuable feature for us is that we
dont have to do anything. CF already provide the out of the box facility to
give us routing logs, so if we can piggy back on that for what we are
interested in we dont have to add libraries to our apps to log interesting
headers on the side.

On Wed, Jul 22, 2015 at 12:45 AM, Shannon Coen <scoen(a)> wrote:

I don't see the difference between WAKAWAKA and X-Cf-Requestid. Gorouter
would have to add some header with a uuid for the request. Your apps have
to have logic to pass this header on, so that a log search returns the
original request as well as subsequent requests between apps. Could you
please clarify?

Thank you,

Shannon Coen
Product Manager, Cloud Foundry
Pivotal, Inc.

On Tue, Jul 21, 2015 at 11:09 AM, Simon Johansson <
simon(a)> wrote:

Sure that header can be used. But then we are adding CF specific stuff
into the implementation of our services, which is something we want to
avoid at all costs.
Also Im not entirely sure if all the libraries we use for Zipkin
supports using custom headers.

All our public apps are fronted by different CDNs, which sets headers
that we might want to store for debugging, so we still need a way to pass
those trough into the log.

On Tuesday, 21 July 2015, Shannon Coen <scoen(a)> wrote:

Hello Simon,

The X-Cf-Requestid header already provides a uuid. Couldn't app "a" add
the value of X-Cf-Requestid to a header of your choosing? Call it WAKAWAKA
or X-Random-Header, but it doesn't need to be a platform standard. Wouldn't
a search for the value of X-Cf-Requestid then provide the desired results?

Thank you,

Shannon Coen
Product Manager, Cloud Foundry
Pivotal, Inc.

On Tue, Jul 21, 2015 at 6:06 AM, Simon Johansson <
simon(a)> wrote:


We have some devs who want to be able to trace a request troughout
their applications.

user -> a -> b -> c
|-> d -> e

When a user makes a request to "a" uuid is generated inside the app,
and the request to "b" from "a" will set a header(call it WAKAWAKA to
uuid), "b"'s call will passthrough WAKAWAKA to "c" and "d", "d" will
passthrough WAKAWAKA to "e". Etc.

We aggregate all RTR logs into ELK so it would be super helpful to
them to be able to filter on WAKAWAKA and get all the access logs(and app
logs aswell, they mostly use GELF so its easy for them to add whatewher
field they want) from the services involved.

I had a quick peek at the gorouter(
and it seems like this should be a simple PR.

1. To gorouter.yml add
- X-Random-Header

2. In makeRecord at the bottom add something like(in psuedo)

data = {}
for header in passthrough_headers:
header_val = r.FormatRequestHeader("X-Forwarded-For")
if header_val:
passthrough_headers[header] = header_val

if data:
fmt.Fprintf(b, data.to_stringified_json())

That would yield a log line like - [21/07/2015:10:17:05 +0000] "GET
HTTP/1.1" 200 0 17 "-" "NING/1.0"
x_forwarded_for:"-" vcap_request_id:1e58195a-cde6-4afd-7f03-43061c9ea91c
response_time:0.004927106 app_id:9784cd03-050d-4b74-9e90-5f17134a3f08
{"WAKAWAKA": "Space is the place", "X-Random-Header": "Once upon a midnight
dreary, while I pondered weak and weary"}

The reason for a stringified JSON is to make it easy to parse with
logstash or other loganalysis tools.

Before I spend time implementing, is this something you would merge?

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