HAProxy rewrite HTTP requests based on HTTP method - load-balancing

Question

I have REST API.
For the sake of simplicity lets say I have two services:
read.request.com
write.request.com
How I can rewrite all read requests (GET method) to read.request.com and all write requests (POST, PUT, DELETE methods) to write.request.com with HAProxy?

Answer 1

Not quite sure which of these is applicable for your situation but hopefully one is.
One Backend
I think this is your situation.
frontend http-in
bind *:80
acl is_post method POST
acl is_get method GET
http-request set-header Host write.request.com if is_post
http-request set-header Host read.request.com if is_get
default_backend api
backend api
server one localhost:8080 check
All this does is check which method is being used and sets the Host header accordingly before passing the request on to localhost:8080.
Two Backends
In this set up you have have one instance of the code running for just read requests and another instance just for write requests. In this case the read code is running on localhost:8080 and the write code is running on localhost:8081.
frontend http-in
bind *:80
acl is_post method POST
acl is_get method GET
use_backend write if is_post
use_backend read if is_get
backend write
http-request set-header Host write.request.com #optional
server write_one localhost:8081 check
backend read
http-request set-header Host read.request.com #optional
server read_one localhost:8080 check
This option starts the same as the previous one by checking which method is being used but instead of using one HAProxy backend it splits out into two. The http-request line inside each backend is optional for this configuration.
Hope that helps.