Docker link between varnish and wordpress not working - wordpress

Question

This is my docker-compose file:
version: '2'
services:
db:
image: mysql:5.7
volumes:
- db_data:/var/lib/mysql
restart: always
environment:
MYSQL_ROOT_PASSWORD: wordpress
MYSQL_DATABASE: wordpress
MYSQL_USER: wordpress
MYSQL_PASSWORD: wordpress
wordpress:
depends_on:
- db
image: wordpress:latest
ports:
- "8000:80"
restart: always
environment:
WORDPRESS_DB_HOST: db:3306
WORDPRESS_DB_PASSWORD: wordpress
varnish:
image: eeacms/varnish
depends_on:
- wordpress
ports:
- 9000:6081
environment:
DNS_ENABLED: "true"
BACKENDS: wordpress
BACKENDS_PORT: 80
volumes:
db_data:
wordpress is running on 0.0.0.0:8080 and on 172.17.0.1:8080
But the /etc/hosts of varnish container is like this
root#4cc3dc214d69:/# cat /etc/hosts
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
172.17.0.3 wordpress fd3f01c29d6a dockoor_wordpress_1
172.17.0.3 wordpress_1 fd3f01c29d6a dockoor_wordpress_1
172.17.0.3 dockoor_wordpress_1 fd3f01c29d6a
172.17.0.4 4cc3dc214d69
varnish is mapping wordpress to 172.17.0.3
That why while trying to access 0.0.0.0:8000 i get
Error 503 Backend fetch failed
Backend fetch failed
Guru Meditation:
XID: 3
Varnish cache server
Can someone please point out whats wrong with my compose file?
P.S docker-compose log shows that varnish do hit worpress but its getting a 302 response.
02 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:19 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:20 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:21 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:22 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:23 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:24 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:25 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:26 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:27 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:29 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:30 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:31 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:32 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:33 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:34 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:35 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:36 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:37 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:38 +0000] "GET / HTTP/1.1" 302 338 "-" "-"
wordpress_1 | 172.17.0.4 - - [25/Mar/2017:10:45:39 +0000] "G

Answer 1

Your link appears to be working as expected. 0.0.0.0 is not an IP address you connect to, that's a listener IP that tells the networking stack to listen on all interfaces rather than a specific IP on the host. In your case, all IP's includes 127.0.0.1 (loopback inside the container) and 172.17.0.3 (the IP reachable by other containers on that network.
Note that links are largely deprecated, it's preferred to configure the containers on a network (other than the default bridge) and use the built in DNS discovery. Similarly, compose version 1 file formats are also largely deprecated, you should consider upgrading to at least the version 2 compose file format. With that format, a network will be created by default for your containers to communicate.
Here's an example of your compose file in version 2 format:
version: '2'
services:
wordpress:
image: wordpress
ports:
- 8080:80
mysql:
image: mariadb
environment:
MYSQL_ROOT_PASSWORD: examplepass
varnish:
image: eeacms/varnish
ports:
- "8000:6081"
environment:
DNS_ENABLED: "true"
BACKENDS: "wordpress"
BACKENDS_PORT: 8080
The http 302 is a redirect, whatever you are running is able to see the url but isn't following the redirect or wordpress is not configured to give a correct redirect.
Update: The varnish error you are seeing is because you are probing / on the wordpress server which is responding with a 302 redirect. Varnish appears to need a 200 success code for the url it is probing. For that, you can add a variable like the following to your varnish environment:
BACKENDS_PROBE_URL: /wp-includes/js/jquery/jquery.js