Running Celery Flower behind Ambassador/Envoy reverse proxy - celery

Question

I am trying to route to a flower server from an emissary/ambassador proxy with a root path different from /. Under the hood this is just an envoy front proxy.
There is an example of running celery flower behind nginx, but I am unable to replicate the same thing with ambassador.
My ambassador Mapping object is
apiVersion: getambassador.io/v2
generation: 16
host: strand.dev.REDACTED.info
kind: Mapping
metadata_labels:
ambassador_crd: strand-flower.front-proxy-internal
name: strand-flower
namespace: front-proxy-internal
prefix: /flower/
regex_rewrite:
pattern: ^/flower/(.*)$
substitution: /\1
service: http://strand-flower.default.svc.cluster.local:80
Which ends in an envoy configuration of
{
"match": {
"case_sensitive": true,
"headers": [
{
"exact_match": "strand.dev.REDACTED.info",
"name": ":authority"
}
],
"prefix": "/flower/",
"runtime_fraction": {
"default_value": {
"denominator": "HUNDRED",
"numerator": 100
},
"runtime_key": "routing.traffic_shift.cluster_http___strand_flower_default_svc-0"
}
},
"route": {
"cluster": "cluster_http___strand_flower_default_svc-0",
"priority": null,
"regex_rewrite": {
"pattern": {
"google_re2": {
"max_program_size": 200
},
"regex": "^/flower/(.*)$"
},
"substitution": "/\\1" <<< Is this supposed to be escaped?
},
"timeout": "3.000s"
}
}
This results in the static assets not being served
However, it looks like the path is not actually being rewritten because I need to go to
$HOSTNAME/flower/flower/ to get to the root, or to $HOSTNAME/flower/flower/task to get to the task part of the dashboard.
The flower server is started with --url_prefix=flower per the documentation here.
How do I get flower to work behind Ambassador?
nginx example
server {
location /flower/static {
alias /the/path/to/flower/static;
}
location /flower {
rewrite ^/flower/(.*)$ /$1 break;
proxy_pass http://localhost:5555;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host $host;
}
}

Answer 1

Answering my own question in-case anyone comes across this.
The problem is that you don't want the rewrite rule listed in the documentation.
You want an ambassador mapping that looks like this
---
apiVersion: getambassador.io/v2
kind: Mapping
metadata:
name: strand-flower
spec:
prefix: /flower/
rewrite: /flower/
service: http://strand-flower.default.svc.cluster.local:80
host: "strand.dev.REDACTED.info"
The docs recommend that you rewrite rewrite /flower/thing/ -> /thing/, but instead you just want to pass the path through and make sure to set --url_prefix=flower when starting your flower server.