How to use Envoy as a Reverse Proxy for a specific URL on localhost - reverse-proxy

Question

I want to use Envoy as a reverse proxy in which I want to redirect the request from
http://example.com:3443/node-exporter/metrics
to
http://localhost:9100/metrics
I want to redirect to a specific URL /metrics on the port 9100.
This is my current envoy_conf.yaml file
listeners:
- name: prom_listener
address:
socket_address : {address: 0.0.0.0, port_value: 3443}
filter_chains:
- name: prom_filter_chain
filters:
- name: envoy.filters.network.http_connection_manager
typed_config:
"#type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
stat_prefix: http_connection_manager
route_config:
virtual_hosts:
- name: prom_local_host
domains: ["*"]
routes:
- name: node-exporter-route
match: {prefix: "/node-exporter/"}
route:
cluster: node-exporter-cluster-server
timeout: 0s
idle_timeout: 0s
http_filters:
- name: envoy.filters.http.router
typed_config:
"#type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router
clusters:
- name: node-exporter-cluster-server
type: static
connect_timeout: 2s
load_assignment:
cluster_name: node-exporter-cluster-server
endpoints:
- lb_endpoints:
- endpoint:
address:
socket_address:
address: 127.0.0.1
port_value: 9100
What changes (additions/deletions) should I make in this in order to achieve the reverse proxying to a specific url on the localhost and port mentioned?

Answer 1

With your configuration, when you are requesting example.com:3443/node-exporter/metrics, you are actually trying to access 127.0.0.1:9100/node-exporter/metrics, which does not exist.
To access 127.0.0.1:9100/metrics (notice the missing /node-exporter part of the URL), you only have to configure your route to tell Envoy to rewrite the prefix. You should use the prefix_rewrite option to strip the /node-exporter part:
routes:
- name: node-exporter-route
match: {prefix: "/node-exporter/"}
route:
cluster: node-exporter-cluster-server
prefix_rewrite: "/"
timeout: 0s
idle_timeout: 0s