Is there a way to push the message to two backends in the async agent? - rabbitmq

Question

(As context, I am using RabbitMQ as the message broker, integrated by KrakenD. The APIs are using Nestjs.)
I understand that the async agent in KrakenD can push the data consumed to multiple backends:
KrakenD contacts the defined backend(s) list passing the event data when a new message kicks in.
However, passing two different backends here result to logger indicating a context exceeded for both of the APIs. If I just put a single backend in the list, it returns what's expected.
Here's the working code:
"backend": [
{
"url_pattern": "/newOrder",
"method": "POST",
"host": [ "http://127.0.0.1:3300" ],
"disable_host_sanitize": false,
"extra_config": {
"modifier/martian": {
"header.Modifier": {
"scope": [
"request"
],
"name": "Content-Type",
"value": "application/json"
}
}
}
},
{
"url_pattern": "/newOrderNotification",
"method": "POST",
"host": [ "http://127.0.0.1:3200" ],
"disable_host_sanitize": false,
"extra_config": {
"modifier/martian": {
"header.Modifier": {
"scope": [
"request"
],
"name": "Content-Type",
"value": "application/json"
}
}
}
}
],
Hope I can receive any advice on this. Thanks!

Answer 1

You can connect a single async agent to several backends but KrakenD does not support distributed transactions, so no more than one non-safe backend request (as defined at RFC 2616, section 9) is allowed per pipe. From the documentation (https://www.krakend.io/docs/backends/):
Even though you can use several backends in one endpoint, KrakenD does not allow you to define multiple non-safe (write) backends. This is a (sometimes controversial) design decision to disable the gateway to handle transactions.
If you need to have a write method (POST, PUT, DELETE, PATCH) together with other GET methods, use the sequential proxy and place a maximum of 1 write method at the end of the sequence.
If you want to send a secondary non-safe request, you can add a minimal lua snippet using the http_response helper (https://www.krakend.io/docs/endpoints/lua/#making-additional-requests-http_response) just like this:
{
"extra_config": {
"modifier/lua-proxy": {
"pre": "local r = request.load(); http_response.new('http://127.0.0.1:3200/newOrderNotification', "POST", r:body())"
}
}
}