mirror of https://github.com/docker/docs.git
206 lines
11 KiB
Markdown
206 lines
11 KiB
Markdown
---
|
|
title: Networking overview
|
|
description: Learn how networking works from the container's point of view
|
|
keywords: networking, container, standalone, IP address, DNS resolution
|
|
aliases:
|
|
- /articles/networking/
|
|
- /config/containers/container-networking/
|
|
- /engine/userguide/networking/
|
|
- /engine/userguide/networking/configure-dns/
|
|
- /engine/userguide/networking/default_network/binding/
|
|
- /engine/userguide/networking/default_network/configure-dns/
|
|
- /engine/userguide/networking/default_network/container-communication/
|
|
- /engine/userguide/networking/dockernetworks/
|
|
---
|
|
|
|
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](packet-filtering-firewalls.md).
|
|
|
|
## 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:
|
|
|
|
```console
|
|
$ 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](./drivers/_index.md).
|
|
|
|
## 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.
|
|
|
|
```console
|
|
$ 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`,
|
|
the container doesn't expose any of its ports to the outside world.
|
|
Use the `--publish` or `-p` flag to make a port available to services
|
|
outside of Docker.
|
|
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`) with the publish flag,
|
|
> only the Docker host can access the published container port.
|
|
>
|
|
> ```console
|
|
> $ docker run -p 127.0.0.1:8080:80 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](https://github.com/moby/moby/issues/45610)
|
|
> { .warning }
|
|
{ .important }
|
|
|
|
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](./drivers/bridge.md).
|
|
|
|
## 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](network-tutorial-standalone.md#use-user-defined-bridge-networks)
|
|
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. If the container can't reach any of the IP addresses you specify, it uses Google's public DNS server at `8.8.8.8`. This allows containers to resolve internet domains. |
|
|
| `--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. |
|
|
|
|
### Nameservers with IPv6 addresses
|
|
|
|
If the `/etc/resolv.conf` file on the host system contains one or more
|
|
nameserver entries with an IPv6 address, those nameserver entries get copied
|
|
over to `/etc/resolv.conf` in containers that you run.
|
|
|
|
For containers using musl libc (in other words, Alpine Linux), this results in
|
|
a race condition for hostname lookup. As a result, hostname resolution might
|
|
sporadically fail if the external IPv6 DNS server wins the race condition
|
|
against the embedded DNS server.
|
|
|
|
It's rare that the external DNS server is faster than the embedded one. But
|
|
things like garbage collection, or large numbers of concurrent DNS requests,
|
|
can sometimes result in a round trip to the external server being faster than local
|
|
resolution.
|
|
|
|
### 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](../reference/cli/docker/container/run.md#add-host) in the
|
|
`docker run` reference documentation.
|
|
|
|
## Proxy server
|
|
|
|
If your container needs to use a proxy server, see
|
|
[Use a proxy server](proxy.md).
|