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Jumpa
Jumpa

Reputation: 4419

Docker Bridge Network DNS

I've two containers running on the default docker bridge network. The daemon assign them a "casual" ip on a specific range.

network_mode: bridge -> 172.17.0.X

How can I reach each other via some alias or name?

Upvotes: 1

Views: 3659

Answers (2)

Clarius
Clarius

Reputation: 1419

I was running a Spring Boot jar in one Docker container and wanted to connect to an Oracle database running in another. In the Spring application.properties file I referenced the database url as

spring.datasource.url=jdbc:oracle:thin:@oracle:1521/xepdb1

In my Windows C:\Windows\System32\drivers\etc\hosts file I resolved 'oracle' as the localhost IP so I could run as Java application from Eclipse...

127.0.0.1 oracle

From the docker inspect command I was able to determine the IP address of the Oracle container as 172.17.0.2.

When I ran my Spring Boot container I ran it with the --add-host switch to resolve 'oracle' as the database container's IP address...

docker run --add-host=oracle:172.17.0.2 -p 9090:8080 -dit --name <name> <image>

In my Jenkins post build batch commands I capture the IP of the running database container and pass it to the app container on startup...

for /F %%x in ('docker inspect -f "{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}" oracle-xe') do set ip=%%x
docker run --add-host=oracle:%ip% -p 9090:8080 -dit --name demo demo

Upvotes: 0

Here_2_learn
Here_2_learn

Reputation: 5451

Let's take following containers running with base image Ubuntu:16.04:

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
2461f410228b        ubuntu:16.04        "/bin/bash"         20 minutes ago      Up 20 minutes                           competent_shockley
6da9d8196637        ubuntu:16.04        "/bin/bash"         21 minutes ago      Up 21 minutes                           hungry_mccarthy

Default networks by Docker, to know more about the default networks refer here:

$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
f83800356529        bridge              bridge              local
8169b2246500        host                host                local
b61e4f39c0ec        none                null                local

Let's find out the containers IP address using docker inspect:

$ docker inspect 2461f410228b | grep IPAddress
            "SecondaryIPAddresses": null,
            "IPAddress": "172.18.0.3",
                    "IPAddress": "172.18.0.3",


$ docker inspect 6da9d8196637 | grep IPAddress
            "SecondaryIPAddresses": null,
            "IPAddress": "172.18.0.2",

By default, containers launched in BRIDGE network will be able to access other containers launched in same network. 

root@2461f410228b:/# ping 172.18.0.2
PING 172.18.0.2 (172.18.0.2) 56(84) bytes of data.
64 bytes from 172.18.0.2: icmp_seq=1 ttl=64 time=0.051 ms

As you are looking for reaching the other container using name/alias, add the target container information in the file /etc/hosts to resolve the DNS:

root@2461f410228b:/# 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
172.18.0.3      2461f410228b
172.18.0.2      docker2

Now try to reach target container using the hostname:

root@2461f410228b:/# ping docker2
PING docker2 (172.18.0.2) 56(84) bytes of data.
64 bytes from docker2 (172.18.0.2): icmp_seq=1 ttl=64 time=0.077 ms

I believe this may help to some extent.

Upvotes: 2

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