Networking overview
Container networking refers to the ability for containers to connect to and communicate with each other, or to non-Docker workloads.
Containers have networking enabled by default, and they can make outgoing
connections. A container has no information about what kind of network it's
attached to, or whether their peers are also Docker workloads or not. A
container only sees a network interface with an IP address, a gateway, a
routing table, DNS services, and other networking details. That is, unless the
container uses the none
network driver.
This page describes networking from the point of view of the container,
and the concepts around container networking.
This page doesn't describe OS-specific details about how Docker networks work.
For information about how Docker manipulates iptables
rules on Linux,
see
Packet filtering and firewalls.
User-defined networks
You can create custom, user-defined networks, and connect multiple containers to the same network. Once connected to a user-defined network, containers can communicate with each other using container IP addresses or container names.
The following example creates a network using the bridge
network driver and
running a container in the created network:
$ docker network create -d bridge my-net
$ docker run --network=my-net -itd --name=container3 busybox
Drivers
The following network drivers are available by default, and provide core networking functionality:
Driver | Description |
---|---|
bridge | The default network driver. |
host | Remove network isolation between the container and the Docker host. |
none | Completely isolate a container from the host and other containers. |
overlay | Overlay networks connect multiple Docker daemons together. |
ipvlan | IPvlan networks provide full control over both IPv4 and IPv6 addressing. |
macvlan | Assign a MAC address to a container. |
For more information about the different drivers, see Network drivers overview.
Container networks
In addition to user-defined networks, you can attach a container to another
container's networking stack directly, using the --network container:<name|id>
flag format.
The following flags aren't supported for containers using the container:
networking mode:
--add-host
--hostname
--dns
--dns-search
--dns-option
--mac-address
--publish
--publish-all
--expose
The following example runs a Redis container, with Redis binding to
localhost
, then running the redis-cli
command and connecting to the Redis
server over the localhost
interface.
$ docker run -d --name redis example/redis --bind 127.0.0.1
$ docker run --rm -it --network container:redis example/redis-cli -h 127.0.0.1
Published ports
By default, when you create or run a container using docker create
or docker run
,
containers on bridge networks don't expose any ports to the outside world.
Use the --publish
or -p
flag to make a port available to services
outside the bridge network.
This creates a firewall rule in the host,
mapping a container port to a port on the Docker host to the outside world.
Here are some examples:
Flag value | Description |
---|---|
-p 8080:80 | Map port 8080 on the Docker host to TCP port 80 in the container. |
-p 192.168.1.100:8080:80 | Map port 8080 on the Docker host IP 192.168.1.100 to TCP port 80 in the container. |
-p 8080:80/udp | Map port 8080 on the Docker host to UDP port 80 in the container. |
-p 8080:80/tcp -p 8080:80/udp | Map TCP port 8080 on the Docker host to TCP port 80 in the container, and map UDP port 8080 on the Docker host to UDP port 80 in the container. |
Important
Publishing container ports is insecure by default. Meaning, when you publish a container's ports it becomes available not only to the Docker host, but to the outside world as well.
If you include the localhost IP address (
127.0.0.1
, or::1
) with the publish flag, only the Docker host and its containers can access the published container port.$ docker run -p 127.0.0.1:8080:80 -p '[::1]:8080:80' nginx
Warning
Hosts within the same L2 segment (for example, hosts connected to the same network switch) can reach ports published to localhost. For more information, see moby/moby#45610
If you want to make a container accessible to other containers, it isn't necessary to publish the container's ports. You can enable inter-container communication by connecting the containers to the same network, usually a bridge network.
Ports on the host's IPv6 addresses will map to the container's IPv4 address
if no host IP is given in a port mapping, the bridge network is IPv4-only,
and --userland-proxy=true
(default).
For more information about port mapping, including how to disable it and use direct routing to containers, see packet filtering and firewalls.
IP address and hostname
By default, the container gets an IP address for every Docker network it attaches to. A container receives an IP address out of the IP subnet of the network. The Docker daemon performs dynamic subnetting and IP address allocation for containers. Each network also has a default subnet mask and gateway.
You can connect a running container to multiple networks,
either by passing the --network
flag multiple times when creating the container,
or using the docker network connect
command for already running containers.
In both cases, you can use the --ip
or --ip6
flags to specify the container's IP address on that particular network.
In the same way, a container's hostname defaults to be the container's ID in Docker.
You can override the hostname using --hostname
.
When connecting to an existing network using docker network connect
,
you can use the --alias
flag to specify an additional network alias for the container on that network.
DNS services
Containers use the same DNS servers as the host by default, but you can
override this with --dns
.
By default, containers inherit the DNS settings as defined in the
/etc/resolv.conf
configuration file.
Containers that attach to the default bridge
network receive a copy of this file.
Containers that attach to a
custom network
use Docker's embedded DNS server.
The embedded DNS server forwards external DNS lookups to the DNS servers configured on the host.
You can configure DNS resolution on a per-container basis, using flags for the
docker run
or docker create
command used to start the container.
The following table describes the available docker run
flags related to DNS
configuration.
Flag | Description |
---|---|
--dns | The IP address of a DNS server. To specify multiple DNS servers, use multiple --dns flags. DNS requests will be forwarded from the container's network namespace so, for example, --dns=127.0.0.1 refers to the container's own loopback address. |
--dns-search | A DNS search domain to search non-fully qualified hostnames. To specify multiple DNS search prefixes, use multiple --dns-search flags. |
--dns-opt | A key-value pair representing a DNS option and its value. See your operating system's documentation for resolv.conf for valid options. |
--hostname | The hostname a container uses for itself. Defaults to the container's ID if not specified. |
Custom hosts
Your container will have lines in /etc/hosts
which define the hostname of the
container itself, as well as localhost
and a few other common things. Custom
hosts, defined in /etc/hosts
on the host machine, aren't inherited by
containers. To pass additional hosts into a container, refer to
add entries to
container hosts file in the
docker run
reference documentation.
Proxy server
If your container needs to use a proxy server, see Use a proxy server.