Varnish forwarder

Transparently forwards all requests to multiple Varnish cache servers. Has an option to get the servers' IP addresses from AWS ECS given a cluster and service names.

Build and run

$ go mod download
$ go build -o main .
$ FWD_PROVIDER=static FWD_BACKENDS=http://127.0.0.1:3000,http://127.0.0.1:3001 ./main

In two other terminals launch the two example backends by running:

$ npx http-echo-server 3000

and

$ npx http-echo-server 3001

Sending requests to http://localhost:6081/test will result in the following output.

$ curl -v -X BAN http://localhost:6081/test
*   Trying 127.0.0.1:6081...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 6081 (#0)
> BAN /test HTTP/1.1
> Host: localhost:6081
> User-Agent: curl/7.68.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Mon, 18 Oct 2021 16:08:44 GMT
< Content-Length: 22
< Content-Type: text/plain; charset=utf-8
<
{"statuses":[200,200]}

Docker

There's a Dockerfile which can be built and run as follows:

$ docker build -t varnish-fwd -f Dockerfile .
$ docker run --rm -it -p 6081:6081 -e FWD_PROVIDER=static -e FWD_BACKENDS=http://172.17.0.1:3000,http://172.17.0.1:3001 varnish-fwd

Environment variables

Variable	Default	Description
FWD_PORT	6081	Listen on this port
FWD_PROVIDER	ecs	The provider of backend URLs. Can be ecs, static or file
FWD_REFRESH_INTERVAL	5m	The interval on which to refresh the backends from the provider. Set to "0" to disable refreshing. Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h". See more here
VARNISH_PORT	6081	(for ecs) Port to use for backends
VARNISH_SCHEME	http	(for ecs) Protocol to use for backends
CLUSTER_NAME		(for ecs) Name of the ECS cluster
VARNISH_SERVICE_NAME		(for ecs) Name of the ECS service which has the Varnish tasks
FWD_BACKENDS		(for static) List of backend URLs separated by comma. E.g. http://localhost:3000,http://localhost:3001
FWD_BACKENDS_FILE		(for file) Path to the file that contains list of backend URLs separated by comma. E.g. http://localhost:3000,http://localhost:3001
AWS_PROFILE		(optional) the profile to use when making requests to AWS
AWS_IAM_AUTHENTICATOR_CACHE_FILE		(optional) full path to the file where AWS session credentials will be cached

Sample Environment config string for GoLand build configuration

AWS_PROFILE=myprofile;AWS_IAM_AUTHENTICATOR_CACHE_FILE=.aws-credentials-cache;CLUSTER_NAME=staging;VARNISH_SERVICE_NAME=varnish;FWD_PROVIDER=static;FWD_BACKENDS=http://localhost:3000,http://localhost:3001;VARNISH_SCHEME=https;VARNISH_PORT=6081

You can launch a test HTTP echo server based on NodeJS as follows

$ npx http-echo-server 3000