Reproducing the bug described in https://github.com/mholt/caddy/pull/880

Caddyfile

localhost:80

proxy / server_1:8080 server_2:8080 server_3:8080 {
  policy round_robin
  health_check /healthcheck 1s
}

docker-compose.yml

version: '2'
services:
  server_1:
    build: .
    environment:
      - SERVER_NAME=server_1

  server_2:
    build: .
    environment:
      - SERVER_NAME=server_2

  server_3:
    build: .
    environment:
      - SERVER_NAME=server_3

  caddy:
    image: abiosoft/caddy
    ports:
      - "80:80"
    volumes:
      - ./Caddyfile:/etc/Caddyfile
    depends_on:
      - server_1
      - server_2
      - server_3

Dockerfile

FROM node
COPY server.js .
CMD node server.js

server.js

var http = require('http')

var numRequests = 0

function handleRequest(request, response){
  if(request.url == "/healthcheck"){
    response.end("Healthcheck OK")
  } else {
    numRequests++
    response.end(process.env.SERVER_NAME + ' requests: ' + numRequests);
  }
}

var server = http.createServer(handleRequest)

server.listen(8080);