Networking with standalone containers

Estimated reading time: 18 minutes

This series of tutorials deals with networking for standalone Docker containers. For networking with swarm services, see Networking with swarm services. If you need to learn more about Docker networking in general, see the overview.

This topic includes three different tutorials. You can run each of them on Linux, Windows, or a Mac, but for the last two, you need a second Docker host running elsewhere.

  • Use the default bridge network demonstrates how to use the default bridge network that Docker sets up for you automatically. This network is not the best choice for production systems.

  • Use user-defined bridge networks shows how to create and use your own custom bridge networks, to connect containers running on the same Docker host. This is recommended for standalone containers running in production.

Although overlay networks are generally used for swarm services, Docker 17.06 and higher allow you to use an overlay network for standalone containers. That’s covered as part of the tutorial on using overlay networks.

Use the default bridge network

In this example, you start two different alpine containers on the same Docker host and do some tests to understand how they communicate with each other. You need to have Docker installed and running.

  1. Open a terminal window. List current networks before you do anything else. Here’s what you should see if you’ve never added a network or initialized a swarm on this Docker daemon. You may see different networks, but you should at least see these (the network IDs will be different):

    $ docker network ls
    
    NETWORK ID          NAME                DRIVER              SCOPE
    17e324f45964        bridge              bridge              local
    6ed54d316334        host                host                local
    7092879f2cc8        none                null                local
    

    The default bridge network is listed, along with host and none. The latter two are not fully-fledged networks, but are used to start a container connected directly to the Docker daemon host’s networking stack, or to start a container with no network devices. This tutorial will connect two containers to the bridge network.

  2. Start two alpine containers running ash, which is Alpine’s default shell rather than bash. The -dit flags mean to start the container detached (in the background), interactive (with the ability to type into it), and with a TTY (so you can see the input and output). Since you are starting it detached, you won’t be connected to the container right away. Instead, the container’s ID will be printed. Because you have not specified any --network flags, the containers connect to the default bridge network.

    $ docker run -dit --name alpine1 alpine ash
    
    $ docker run -dit --name alpine2 alpine ash
    

    Check that both containers are actually started:

    $ docker container ls
    
    CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
    602dbf1edc81        alpine              "ash"               4 seconds ago       Up 3 seconds                            alpine2
    da33b7aa74b0        alpine              "ash"               17 seconds ago      Up 16 seconds                           alpine1
    
  3. Inspect the bridge network to see what containers are connected to it.

    $ docker network inspect bridge
    
    [
        {
            "Name": "bridge",
            "Id": "17e324f459648a9baaea32b248d3884da102dde19396c25b30ec800068ce6b10",
            "Created": "2017-06-22T20:27:43.826654485Z",
            "Scope": "local",
            "Driver": "bridge",
            "EnableIPv6": false,
            "IPAM": {
                "Driver": "default",
                "Options": null,
                "Config": [
                    {
                        "Subnet": "172.17.0.0/16",
                        "Gateway": "172.17.0.1"
                    }
                ]
            },
            "Internal": false,
            "Attachable": false,
            "Containers": {
                "602dbf1edc81813304b6cf0a647e65333dc6fe6ee6ed572dc0f686a3307c6a2c": {
                    "Name": "alpine2",
                    "EndpointID": "03b6aafb7ca4d7e531e292901b43719c0e34cc7eef565b38a6bf84acf50f38cd",
                    "MacAddress": "02:42:ac:11:00:03",
                    "IPv4Address": "172.17.0.3/16",
                    "IPv6Address": ""
                },
                "da33b7aa74b0bf3bda3ebd502d404320ca112a268aafe05b4851d1e3312ed168": {
                    "Name": "alpine1",
                    "EndpointID": "46c044a645d6afc42ddd7857d19e9dcfb89ad790afb5c239a35ac0af5e8a5bc5",
                    "MacAddress": "02:42:ac:11:00:02",
                    "IPv4Address": "172.17.0.2/16",
                    "IPv6Address": ""
                }
            },
            "Options": {
                "com.docker.network.bridge.default_bridge": "true",
                "com.docker.network.bridge.enable_icc": "true",
                "com.docker.network.bridge.enable_ip_masquerade": "true",
                "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
                "com.docker.network.bridge.name": "docker0",
                "com.docker.network.driver.mtu": "1500"
            },
            "Labels": {}
        }
    ]
    

    Near the top, information about the bridge network is listed, including the IP address of the gateway between the Docker host and the bridge network (172.17.0.1). Under the Containers key, each connected container is listed, along with information about its IP address (172.17.0.2 for alpine1 and 172.17.0.3 for alpine2).

  4. The containers are running in the background. Use the docker attach command to connect to alpine1.

    $ docker attach alpine1
    
    / #
    

    The prompt changes to # to indicate that you are the root user within the container. Use the ip addr show command to show the network interfaces for alpine1 as they look from within the container:

    # ip addr show
    
    1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
        link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        inet 127.0.0.1/8 scope host lo
           valid_lft forever preferred_lft forever
        inet6 ::1/128 scope host
           valid_lft forever preferred_lft forever
    27: eth0@if28: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue state UP
        link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff
        inet 172.17.0.2/16 scope global eth0
           valid_lft forever preferred_lft forever
        inet6 fe80::42:acff:fe11:2/64 scope link
           valid_lft forever preferred_lft forever
    

    The first interface is the loopback device. Ignore it for now. Notice that the second interface has the IP address 172.17.0.2, which is the same address shown for alpine1 in the previous step.

  5. From within alpine1, make sure you can connect to the internet by pinging google.com. The -c 2 flag limits the command two two ping attempts.

    # ping -c 2 google.com
    
    PING google.com (172.217.3.174): 56 data bytes
    64 bytes from 172.217.3.174: seq=0 ttl=41 time=9.841 ms
    64 bytes from 172.217.3.174: seq=1 ttl=41 time=9.897 ms
    
    --- google.com ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 9.841/9.869/9.897 ms
    
  6. Now try to ping the second container. First, ping it by its IP address, 172.17.0.3:

    # ping -c 2 172.17.0.3
    
    PING 172.17.0.3 (172.17.0.3): 56 data bytes
    64 bytes from 172.17.0.3: seq=0 ttl=64 time=0.086 ms
    64 bytes from 172.17.0.3: seq=1 ttl=64 time=0.094 ms
    
    --- 172.17.0.3 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.086/0.090/0.094 ms
    

    This succeeds. Next, try pinging the alpine2 container by container name. This will fail.

    # ping -c 2 alpine2
    
    ping: bad address 'alpine2'
    
  7. Detach from alpine2 without stopping it by using the detach sequence, CTRL + p CTRL + q (hold down CTRL and type p followed by q). If you wish, attach to alpine2 and repeat steps 4, 5, and 6 there, substituting alpine1 for alpine2.

  8. Stop and remove both containers.

    $ docker container stop alpine1 alpine2
    $ docker container rm alpine1 alpine2
    

Remember, the default bridge network is not recommended for production. To learn about user-defined bridge networks, continue to the next tutorial.

Use user-defined bridge networks

In this example, we again start two alpine containers, but attach them to a user-defined network called alpine-net which we have already created. These containers are not connected to the default bridge network at all. We then start a third alpine container which is connected to the bridge network but not connected to alpine-net, and a fourth alpine container which is connected to both networks.

  1. Create the alpine-net network. You do not need the --driver bridge flag since it’s the default, but this example shows how to specify it.

    $ docker network create --driver bridge alpine-net
    
  2. List Docker’s networks:

    $ docker network ls
    
    NETWORK ID          NAME                DRIVER              SCOPE
    e9261a8c9a19        alpine-net          bridge              local
    17e324f45964        bridge              bridge              local
    6ed54d316334        host                host                local
    7092879f2cc8        none                null                local
    

    Inspect the alpine-net network. This shows you its IP address and the fact that no containers are connected to it:

    $ docker network inspect alpine-net
    
    [
        {
            "Name": "alpine-net",
            "Id": "e9261a8c9a19eabf2bf1488bf5f208b99b1608f330cff585c273d39481c9b0ec",
            "Created": "2017-09-25T21:38:12.620046142Z",
            "Scope": "local",
            "Driver": "bridge",
            "EnableIPv6": false,
            "IPAM": {
                "Driver": "default",
                "Options": {},
                "Config": [
                    {
                        "Subnet": "172.18.0.0/16",
                        "Gateway": "172.18.0.1"
                    }
                ]
            },
            "Internal": false,
            "Attachable": false,
            "Containers": {},
            "Options": {},
            "Labels": {}
        }
    ]
    

    Notice that this network’s gateway is 172.18.0.1, as opposed to the default bridge network, whose gateway is 172.17.0.1. The exact IP address may be different on your system.

  3. Create your four containers. Notice the --network flags. You can only connect to one network during the docker run command, so you need to use docker network attach afterward to connect alpine4 to the bridge network as well.

    $ docker run -dit --name alpine1 --network alpine-net alpine ash
    
    $ docker run -dit --name alpine2 --network alpine-net alpine ash
    
    $ docker run -dit --name alpine3 alpine ash
    
    $ docker run -dit --name alpine4 --network alpine-net alpine ash
    
    $ docker network connect bridge alpine4
    

    Verify that all containers are running:

    $ docker container ls
    
    CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS               NAMES
    156849ccd902        alpine              "ash"               41 seconds ago       Up 41 seconds                           alpine4
    fa1340b8d83e        alpine              "ash"               51 seconds ago       Up 51 seconds                           alpine3
    a535d969081e        alpine              "ash"               About a minute ago   Up About a minute                       alpine2
    0a02c449a6e9        alpine              "ash"               About a minute ago   Up About a minute                       alpine1
    
  4. Inspect the bridge network and the alpine-net network again:

    $ docker network inspect bridge
    
    [
        {
            "Name": "bridge",
            "Id": "17e324f459648a9baaea32b248d3884da102dde19396c25b30ec800068ce6b10",
            "Created": "2017-06-22T20:27:43.826654485Z",
            "Scope": "local",
            "Driver": "bridge",
            "EnableIPv6": false,
            "IPAM": {
                "Driver": "default",
                "Options": null,
                "Config": [
                    {
                        "Subnet": "172.17.0.0/16",
                        "Gateway": "172.17.0.1"
                    }
                ]
            },
            "Internal": false,
            "Attachable": false,
            "Containers": {
                "156849ccd902b812b7d17f05d2d81532ccebe5bf788c9a79de63e12bb92fc621": {
                    "Name": "alpine4",
                    "EndpointID": "7277c5183f0da5148b33d05f329371fce7befc5282d2619cfb23690b2adf467d",
                    "MacAddress": "02:42:ac:11:00:03",
                    "IPv4Address": "172.17.0.3/16",
                    "IPv6Address": ""
                },
                "fa1340b8d83eef5497166951184ad3691eb48678a3664608ec448a687b047c53": {
                    "Name": "alpine3",
                    "EndpointID": "5ae767367dcbebc712c02d49556285e888819d4da6b69d88cd1b0d52a83af95f",
                    "MacAddress": "02:42:ac:11:00:02",
                    "IPv4Address": "172.17.0.2/16",
                    "IPv6Address": ""
                }
            },
            "Options": {
                "com.docker.network.bridge.default_bridge": "true",
                "com.docker.network.bridge.enable_icc": "true",
                "com.docker.network.bridge.enable_ip_masquerade": "true",
                "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
                "com.docker.network.bridge.name": "docker0",
                "com.docker.network.driver.mtu": "1500"
            },
            "Labels": {}
        }
    ]
    

    Containers alpine3 and alpine4 are connected to the bridge network.

    $ docker network inspect alpine-net
    
    [
        {
            "Name": "alpine-net",
            "Id": "e9261a8c9a19eabf2bf1488bf5f208b99b1608f330cff585c273d39481c9b0ec",
            "Created": "2017-09-25T21:38:12.620046142Z",
            "Scope": "local",
            "Driver": "bridge",
            "EnableIPv6": false,
            "IPAM": {
                "Driver": "default",
                "Options": {},
                "Config": [
                    {
                        "Subnet": "172.18.0.0/16",
                        "Gateway": "172.18.0.1"
                    }
                ]
            },
            "Internal": false,
            "Attachable": false,
            "Containers": {
                "0a02c449a6e9a15113c51ab2681d72749548fb9f78fae4493e3b2e4e74199c4a": {
                    "Name": "alpine1",
                    "EndpointID": "c83621678eff9628f4e2d52baf82c49f974c36c05cba152db4c131e8e7a64673",
                    "MacAddress": "02:42:ac:12:00:02",
                    "IPv4Address": "172.18.0.2/16",
                    "IPv6Address": ""
                },
                "156849ccd902b812b7d17f05d2d81532ccebe5bf788c9a79de63e12bb92fc621": {
                    "Name": "alpine4",
                    "EndpointID": "058bc6a5e9272b532ef9a6ea6d7f3db4c37527ae2625d1cd1421580fd0731954",
                    "MacAddress": "02:42:ac:12:00:04",
                    "IPv4Address": "172.18.0.4/16",
                    "IPv6Address": ""
                },
                "a535d969081e003a149be8917631215616d9401edcb4d35d53f00e75ea1db653": {
                    "Name": "alpine2",
                    "EndpointID": "198f3141ccf2e7dba67bce358d7b71a07c5488e3867d8b7ad55a4c695ebb8740",
                    "MacAddress": "02:42:ac:12:00:03",
                    "IPv4Address": "172.18.0.3/16",
                    "IPv6Address": ""
                }
            },
            "Options": {},
            "Labels": {}
        }
    ]
    

    Containers alpine1, alpine2, and alpine4 are connected to the alpine-net network.

  5. On user-defined networks like alpine-net, containers can not only communicate by IP address, but can also resolve a container name to an IP address. This capability is called automatic service discovery. Let’s connect to alpine1 and test this out. alpine1 should be able to resolve alpine2 and alpine4 (and alpine1, itself) to IP addresses.

    $ docker container attach alpine1
    
    # ping -c 2 alpine2
    
    PING alpine2 (172.18.0.3): 56 data bytes
    64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.085 ms
    64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.090 ms
    
    --- alpine2 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.085/0.087/0.090 ms
    
    # ping -c 2 alpine4
    
    PING alpine4 (172.18.0.4): 56 data bytes
    64 bytes from 172.18.0.4: seq=0 ttl=64 time=0.076 ms
    64 bytes from 172.18.0.4: seq=1 ttl=64 time=0.091 ms
    
    --- alpine4 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.076/0.083/0.091 ms
    
    # ping -c 2 alpine1
    
    PING alpine1 (172.18.0.2): 56 data bytes
    64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.026 ms
    64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.054 ms
    
    --- alpine1 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.026/0.040/0.054 ms
    
  6. From alpine1, you should not be able to connect to alpine3 at all, since it is not on the alpine-net network.

    # ping -c 2 alpine3
    
    ping: bad address 'alpine3'
    

    Not only that, but you can’t connect to alpine3 from alpine1 by its IP address either. Look back at the docker network inspect output for the bridge network and find alpine3’s IP address: 172.17.0.2 Try to ping it.

    # ping -c 2 172.17.0.2
    
    PING 172.17.0.2 (172.17.0.2): 56 data bytes
    
    --- 172.17.0.2 ping statistics ---
    2 packets transmitted, 0 packets received, 100% packet loss
    

    Detach from alpine1 using detach sequence, CTRL + p CTRL + q (hold down CTRL and type p followed by q).

  7. Remember that alpine4 is connected to both the default bridge network and alpine-net. It should be able to reach all of the other containers. However, you will need to address alpine3 by its IP address. Attach to it and run the tests.

    $ docker container attach alpine4
    
    # ping -c 2 alpine1
    
    PING alpine1 (172.18.0.2): 56 data bytes
    64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.074 ms
    64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.082 ms
    
    --- alpine1 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.074/0.078/0.082 ms
    
    # ping -c 2 alpine2
    
    PING alpine2 (172.18.0.3): 56 data bytes
    64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.075 ms
    64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.080 ms
    
    --- alpine2 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.075/0.077/0.080 ms
    
    # ping -c 2 alpine3
    ping: bad address 'alpine3'
    
    # ping -c 2 172.17.0.2
    
    PING 172.17.0.2 (172.17.0.2): 56 data bytes
    64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.089 ms
    64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.075 ms
    
    --- 172.17.0.2 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.075/0.082/0.089 ms
    
    # ping -c 2 alpine4
    
    PING alpine4 (172.18.0.4): 56 data bytes
    64 bytes from 172.18.0.4: seq=0 ttl=64 time=0.033 ms
    64 bytes from 172.18.0.4: seq=1 ttl=64 time=0.064 ms
    
    --- alpine4 ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 0.033/0.048/0.064 ms
    
  8. As a final test, make sure your containers can all connect to the internet by pinging google.com. You are already attached to alpine4 so start by trying from there. Next, detach from alpine4 and connect to alpine3 (which is only attached to the bridge network) and try again. Finally, connect to alpine1 (which is only connected to the alpine-net network) and try again.

    # ping -c 2 google.com
    
    PING google.com (172.217.3.174): 56 data bytes
    64 bytes from 172.217.3.174: seq=0 ttl=41 time=9.778 ms
    64 bytes from 172.217.3.174: seq=1 ttl=41 time=9.634 ms
    
    --- google.com ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 9.634/9.706/9.778 ms
    
    CTRL+p CTRL+q
    
    $ docker container attach alpine3
    
    # ping -c 2 google.com
    
    PING google.com (172.217.3.174): 56 data bytes
    64 bytes from 172.217.3.174: seq=0 ttl=41 time=9.706 ms
    64 bytes from 172.217.3.174: seq=1 ttl=41 time=9.851 ms
    
    --- google.com ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 9.706/9.778/9.851 ms
    
    CTRL+p CTRL+q
    
    $ docker container attach alpine1
    
    # ping -c 2 google.com
    
    PING google.com (172.217.3.174): 56 data bytes
    64 bytes from 172.217.3.174: seq=0 ttl=41 time=9.606 ms
    64 bytes from 172.217.3.174: seq=1 ttl=41 time=9.603 ms
    
    --- google.com ping statistics ---
    2 packets transmitted, 2 packets received, 0% packet loss
    round-trip min/avg/max = 9.603/9.604/9.606 ms
    
    CTRL+p CTRL+q
    
  9. Stop and remove all containers and the alpine-net network.

    $ docker container stop alpine1 alpine2 alpine3 alpine4
    
    $ docker container rm alpine1 alpine2 alpine3 alpine4
    
    $ docker network rm alpine-net
    

Other networking tutorials

Now that you have completed the networking tutorials for standalone containers, you might want to run through these other networking tutorials:

networking, bridge, routing, ports, overlay