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@@ -6,18 +6,16 @@ page_keywords: Examples, Usage, links, linking, docker, documentation, examples,
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## Introduction
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-From version 0.6.5 you are now able to `name` a container and `link` it to
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-another container by referring to its name. This will create a parent -> child
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-relationship where the parent container can see selected information about its
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-child.
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+From version 0.6.5 you are now able to `name` a container and `link` it
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+to another container by referring to its name. This will create a parent
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+-> child relationship where the parent container can see selected
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+information about its child.
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## Container Naming
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-New in version v0.6.5.
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-
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-You can now name your container by using the `--name` flag. If no name is
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-provided, Docker will automatically generate a name. You can see this name
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-using the `docker ps` command.
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+You can now name your container by using the `--name` flag. If no name
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+is provided, Docker will automatically generate a name. You can see this
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+name using the `docker ps` command.
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# format is "sudo docker run --name <container_name> <image_name> <command>"
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$ sudo docker run --name test ubuntu /bin/bash
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@@ -29,48 +27,49 @@ using the `docker ps` command.
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## Links: service discovery for docker
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-New in version v0.6.5.
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-
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Links allow containers to discover and securely communicate with each
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-other by using the flag `-link name:alias`. Inter-container communication
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-can be disabled with the daemon flag `-icc=false`. With this flag set to
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-`false`, Container A cannot access Container unless explicitly allowed via
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-a link. This is a huge win for securing your containers. When two containers
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-are linked together Docker creates a parent child relationship between the
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-containers. The parent container will be able to access information via
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-environment variables of the child such as name, exposed ports, IP and other
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-selected environment variables.
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-
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-When linking two containers Docker will use the exposed ports of the container
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-to create a secure tunnel for the parent to access. If a database container
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-only exposes port 8080 then the linked container will only be allowed to access
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-port 8080 and nothing else if inter-container communication is set to false.
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-
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-For example, there is an image called `crosbymichael/redis` that exposes the
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-port 6379 and starts the Redis server. Let's name the container as `redis`
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-based on that image and run it as daemon.
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+other by using the flag `-link name:alias`. Inter-container
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+communication can be disabled with the daemon flag `-icc=false`. With
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+this flag set to `false`, Container A cannot access Container unless
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+explicitly allowed via a link. This is a huge win for securing your
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+containers. When two containers are linked together Docker creates a
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+parent child relationship between the containers. The parent container
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+will be able to access information via environment variables of the
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+child such as name, exposed ports, IP and other selected environment
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+variables.
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+
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+When linking two containers Docker will use the exposed ports of the
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+container to create a secure tunnel for the parent to access. If a
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+database container only exposes port 8080 then the linked container will
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+only be allowed to access port 8080 and nothing else if inter-container
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+communication is set to false.
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+
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+For example, there is an image called `crosbymichael/redis` that exposes
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+the port 6379 and starts the Redis server. Let's name the container as
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+`redis` based on that image and run it as daemon.
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$ sudo docker run -d --name redis crosbymichael/redis
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-We can issue all the commands that you would expect using the name `redis`;
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-start, stop, attach, using the name for our container. The name also allows
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-us to link other containers into this one.
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+We can issue all the commands that you would expect using the name
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+`redis`; start, stop, attach, using the name for our container. The name
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+also allows us to link other containers into this one.
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-Next, we can start a new web application that has a dependency on Redis and
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-apply a link to connect both containers. If you noticed when running our Redis
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-server we did not use the `-p` flag to publish the Redis port to the host
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-system. Redis exposed port 6379 and this is all we need to establish a link.
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+Next, we can start a new web application that has a dependency on Redis
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+and apply a link to connect both containers. If you noticed when running
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+our Redis server we did not use the `-p` flag to publish the Redis port
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+to the host system. Redis exposed port 6379 and this is all we need to
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+establish a link.
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$ sudo docker run -t -i --link redis:db --name webapp ubuntu bash
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When you specified `--link redis:db` you are telling Docker to link the
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container named `redis` into this new container with the alias `db`.
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-Environment variables are prefixed with the alias so that the parent container
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-can access network and environment information from the containers that are
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-linked into it.
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+Environment variables are prefixed with the alias so that the parent
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+container can access network and environment information from the
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+containers that are linked into it.
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-If we inspect the environment variables of the second container, we would see
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-all the information about the child container.
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+If we inspect the environment variables of the second container, we
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+would see all the information about the child container.
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$ root@4c01db0b339c:/# env
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@@ -90,20 +89,20 @@ all the information about the child container.
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_=/usr/bin/env
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root@4c01db0b339c:/#
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-Accessing the network information along with the environment of the child
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-container allows us to easily connect to the Redis service on the specific
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-IP and port in the environment.
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+Accessing the network information along with the environment of the
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+child container allows us to easily connect to the Redis service on the
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+specific IP and port in the environment.
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> **Note**:
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> These Environment variables are only set for the first process in the
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> container. Similarly, some daemons (such as `sshd`)
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> will scrub them when spawning shells for connection.
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-You can work around this by storing the initial `env` in a file, or looking
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-at `/proc/1/environ`.
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+You can work around this by storing the initial `env` in a file, or
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+looking at `/proc/1/environ`.
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-Running `docker ps` shows the 2 containers, and the `webapp/db` alias name for
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-the Redis container.
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+Running `docker ps` shows the 2 containers, and the `webapp/db` alias
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+name for the Redis container.
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$ docker ps
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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@@ -112,13 +111,13 @@ the Redis container.
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## Resolving Links by Name
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-New in version v0.11.
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+> *Note:* New in version v0.11.
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Linked containers can be accessed by hostname. Hostnames are mapped by
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appending entries to '/etc/hosts' using the linked container's alias.
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-For example, linking a container using '--link redis:db' will generate the
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-following '/etc/hosts' file:
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+For example, linking a container using '--link redis:db' will generate
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+the following '/etc/hosts' file:
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root@6541a75d44a0:/# cat /etc/hosts
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172.17.0.3 6541a75d44a0
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James Turnbull