mirror of https://github.com/docker/docs.git
85 lines
6.2 KiB
Markdown
85 lines
6.2 KiB
Markdown
---
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title: Container networking
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description: How networking works from the container's point of view
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keywords: networking, container, standalone
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redirect_from:
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- /engine/userguide/networking/configure-dns/
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- /engine/userguide/networking/default_network/configure-dns/
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- /engine/userguide/networking/default_network/binding/
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- /engine/userguide/networking/default_network/container-communication/
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---
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A container has no information about what kind of network it's attached to,
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whether it's a [bridge](../../network/bridge.md), an [overlay](../../network/overlay.md),
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a [macvlan network](../../network/macvlan.md), or a custom network plugin.
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A container only sees a network interface with an IP address,
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a gateway, a routing table, DNS services, and other networking details.
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That is, unless the container uses the `none` network driver.
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This page describes networking from the point of view of the container.
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## Published ports
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By default, when you create or run a container using `docker create` or `docker run`,
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the container doesn't expose any of its ports to the outside world.
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To make a port available to services outside of Docker,
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or to Docker containers running on a different network,
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use the `--publish` or `-p` flag.
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This creates a firewall rule in the container,
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mapping a container port to a port on the Docker host to the outside world.
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Here are some examples:
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| Flag value | Description |
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| ------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- |
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| `-p 8080:80` | Map TCP port 80 in the container to port `8080` on the Docker host. |
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| `-p 192.168.1.100:8080:80` | Map TCP port 80 in the container to port `8080` on the Docker host for connections to host IP `192.168.1.100`. |
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| `-p 8080:80/udp` | Map UDP port 80 in the container to port `8080` on the Docker host. |
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| `-p 8080:80/tcp -p 8080:80/udp` | Map TCP port 80 in the container to TCP port `8080` on the Docker host, and map UDP port `80` in the container to UDP port `8080` on the Docker host. |
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## IP address and hostname
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By default, the container gets an IP address for every Docker network it attaches to.
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A container receives an IP address out of the IP pool of the network it attaches to.
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The Docker daemon effectively acts as a DHCP server for each container.
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Each network also has a default subnet mask and gateway.
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When a container starts, it can only attach to a single network, using the `--network` flag.
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You can connect a running container to multiple networks using the `docker network connect` command.
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When you start a container using the `--network` flag,
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you can specify the IP address for the container on that network using the `--ip` or `--ip6` flags.
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When you connect an existing container to a different network using `docker network connect`,
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you can use the `--ip` or `--ip6` flags on that command
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to specify the container's IP address on the additional network.
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In the same way, a container's hostname defaults to be the container's ID in Docker.
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You can override the hostname using `--hostname`.
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When connecting to an existing network using `docker network connect`,
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you can use the `--alias` flag to specify an additional network alias for the container on that network.
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## DNS services
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By default, containers inherit the DNS settings of the host, as defined in the `/etc/resolv.conf` configuration file.
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Containers that attach to the default `bridge` network receive a copy of this file.
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Containers that attach to a
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[custom network](../../network/network-tutorial-standalone.md#use-user-defined-bridge-networks)
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use Docker's embedded DNS server.
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The embedded DNS server forwards external DNS lookups to the DNS servers configured on the host.
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Custom hosts, defined in `/etc/hosts` on the host machine, aren't inherited by containers.
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To pass additional hosts into container, refer to
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[add entries to container hosts file](../../engine/reference/commandline/run.md#add-host)
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in the `docker run` reference documentation.
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You can override these settings on a per-container basis.
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| Flag | Description |
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| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| `--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. |
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| `--dns-search` | A DNS search domain to search non-fully-qualified hostnames. To specify multiple DNS search prefixes, use multiple `--dns-search` flags. |
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| `--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. |
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| `--hostname` | The hostname a container uses for itself. Defaults to the container's ID if not specified. |
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## Proxy server
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If your container needs to use a proxy server, see
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[Use a proxy server](../../network/proxy.md).
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