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Addresses #7985 Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
322 lines
11 KiB
Markdown
322 lines
11 KiB
Markdown
page_title: Working with Containers
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page_description: Learn how to manage and operate Docker containers.
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page_keywords: docker, the docker guide, documentation, docker.io, monitoring containers, docker top, docker inspect, docker port, ports, docker logs, log, Logs
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# Working with Containers
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In the [last section of the Docker User Guide](/userguide/dockerizing)
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we launched our first containers. We launched two containers using the
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`docker run` command.
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* Containers we ran interactively in the foreground.
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* One container we ran daemonized in the background.
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In the process we learned about several Docker commands:
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* `docker ps` - Lists containers.
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* `docker logs` - Shows us the standard output of a container.
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* `docker stop` - Stops running containers.
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> **Tip:**
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> Another way to learn about `docker` commands is our
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> [interactive tutorial](https://www.docker.com/tryit/).
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The `docker` client is pretty simple. Each action you can take
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with Docker is a command and each command can take a series of
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flags and arguments.
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# Usage: [sudo] docker [flags] [command] [arguments] ..
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# Example:
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$ docker run -i -t ubuntu /bin/bash
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Let's see this in action by using the `docker version` command to return
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version information on the currently installed Docker client and daemon.
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$ sudo docker version
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This command will not only provide you the version of Docker client and
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daemon you are using, but also the version of Go (the programming
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language powering Docker).
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Client version: 0.8.0
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Go version (client): go1.2
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Git commit (client): cc3a8c8
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Server version: 0.8.0
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Git commit (server): cc3a8c8
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Go version (server): go1.2
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Last stable version: 0.8.0
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### Seeing what the Docker client can do
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We can see all of the commands available to us with the Docker client by
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running the `docker` binary without any options.
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$ sudo docker
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You will see a list of all currently available commands.
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Commands:
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attach Attach to a running container
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build Build an image from a Dockerfile
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commit Create a new image from a container's changes
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. . .
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### Seeing Docker command usage
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You can also zoom in and review the usage for specific Docker commands.
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Try typing Docker followed with a `[command]` to see the usage for that
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command:
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$ sudo docker attach
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Help output . . .
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Or you can also pass the `--help` flag to the `docker` binary.
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$ sudo docker attach --help
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This will display the help text and all available flags:
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Usage: docker attach [OPTIONS] CONTAINER
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Attach to a running container
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--no-stdin=false: Do not attach stdin
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--sig-proxy=true: Proxify all received signal to the process (even in non-tty mode)
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> **Note:**
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> You can see a full list of Docker's commands
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> [here](/reference/commandline/cli/).
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## Running a Web Application in Docker
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So now we've learnt a bit more about the `docker` client let's move onto
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the important stuff: running more containers. So far none of the
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containers we've run did anything particularly useful though. So let's
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build on that experience by running an example web application in
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Docker.
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For our web application we're going to run a Python Flask application.
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Let's start with a `docker run` command.
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$ sudo docker run -d -P training/webapp python app.py
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Let's review what our command did. We've specified two flags: `-d` and
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`-P`. We've already seen the `-d` flag which tells Docker to run the
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container in the background. The `-P` flag is new and tells Docker to
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map any required network ports inside our container to our host. This
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lets us view our web application.
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We've specified an image: `training/webapp`. This image is a
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pre-built image we've created that contains a simple Python Flask web
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application.
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Lastly, we've specified a command for our container to run: `python app.py`.
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This launches our web application.
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> **Note:**
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> You can see more detail on the `docker run` command in the [command
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> reference](/reference/commandline/cli/#run) and the [Docker Run
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> Reference](/reference/run/).
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## Viewing our Web Application Container
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Now let's see our running container using the `docker ps` command.
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$ sudo docker ps -l
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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bc533791f3f5 training/webapp:latest python app.py 5 seconds ago Up 2 seconds 0.0.0.0:49155->5000/tcp nostalgic_morse
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You can see we've specified a new flag, `-l`, for the `docker ps`
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command. This tells the `docker ps` command to return the details of the
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*last* container started.
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> **Note:**
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> By default, the `docker ps` command only shows information about running
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> containers. If you want to see stopped containers too use the `-a` flag.
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We can see the same details we saw [when we first Dockerized a
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container](/userguide/dockerizing) with one important addition in the `PORTS`
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column.
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PORTS
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0.0.0.0:49155->5000/tcp
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When we passed the `-P` flag to the `docker run` command Docker mapped any
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ports exposed in our image to our host.
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> **Note:**
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> We'll learn more about how to expose ports in Docker images when
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> [we learn how to build images](/userguide/dockerimages).
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In this case Docker has exposed port 5000 (the default Python Flask
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port) on port 49155.
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Network port bindings are very configurable in Docker. In our last
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example the `-P` flag is a shortcut for `-p 5000` that maps port 5000
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inside the container to a high port (from the range 49153 to 65535) on
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the local Docker host. We can also bind Docker containers to specific
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ports using the `-p` flag, for example:
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$ sudo docker run -d -p 5000:5000 training/webapp python app.py
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This would map port 5000 inside our container to port 5000 on our local
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host. You might be asking about now: why wouldn't we just want to always
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use 1:1 port mappings in Docker containers rather than mapping to high
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ports? Well 1:1 mappings have the constraint of only being able to map
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one of each port on your local host. Let's say you want to test two
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Python applications: both bound to port 5000 inside your container.
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Without Docker's port mapping you could only access one at a time.
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So let's now browse to port 49155 in a web browser to
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see the application.
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.
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Our Python application is live!
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> **Note:**
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> If you have used the boot2docker virtual machine on OS X, Windows or Linux,
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> you'll need to get the IP of the virtual host instead of using localhost.
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> You can do this by running the following in
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> the boot2docker shell.
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>
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> $ boot2docker ip
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> The VM's Host only interface IP address is: 192.168.59.103
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>
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> In this case you'd browse to http://192.168.59.103:49155 for the above example.
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## A Network Port Shortcut
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Using the `docker ps` command to return the mapped port is a bit clumsy so
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Docker has a useful shortcut we can use: `docker port`. To use `docker port` we
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specify the ID or name of our container and then the port for which we need the
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corresponding public-facing port.
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$ sudo docker port nostalgic_morse 5000
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0.0.0.0:49155
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In this case we've looked up what port is mapped externally to port 5000 inside
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the container.
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## Viewing the Web Application's Logs
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Let's also find out a bit more about what's happening with our application and
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use another of the commands we've learnt, `docker logs`.
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$ sudo docker logs -f nostalgic_morse
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* Running on http://0.0.0.0:5000/
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10.0.2.2 - - [23/May/2014 20:16:31] "GET / HTTP/1.1" 200 -
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10.0.2.2 - - [23/May/2014 20:16:31] "GET /favicon.ico HTTP/1.1" 404 -
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This time though we've added a new flag, `-f`. This causes the `docker
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logs` command to act like the `tail -f` command and watch the
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container's standard out. We can see here the logs from Flask showing
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the application running on port 5000 and the access log entries for it.
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## Looking at our Web Application Container's processes
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In addition to the container's logs we can also examine the processes
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running inside it using the `docker top` command.
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$ sudo docker top nostalgic_morse
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PID USER COMMAND
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854 root python app.py
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Here we can see our `python app.py` command is the only process running inside
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the container.
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## Inspecting our Web Application Container
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Lastly, we can take a low-level dive into our Docker container using the
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`docker inspect` command. It returns a JSON hash of useful configuration
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and status information about Docker containers.
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$ sudo docker inspect nostalgic_morse
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Let's see a sample of that JSON output.
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[{
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"ID": "bc533791f3f500b280a9626688bc79e342e3ea0d528efe3a86a51ecb28ea20",
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"Created": "2014-05-26T05:52:40.808952951Z",
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"Path": "python",
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"Args": [
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"app.py"
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],
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"Config": {
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"Hostname": "bc533791f3f5",
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"Domainname": "",
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"User": "",
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. . .
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We can also narrow down the information we want to return by requesting a
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specific element, for example to return the container's IP address we would:
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$ sudo docker inspect -f '{{ .NetworkSettings.IPAddress }}' nostalgic_morse
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172.17.0.5
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## Stopping our Web Application Container
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Okay we've seen web application working. Now let's stop it using the
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`docker stop` command and the name of our container: `nostalgic_morse`.
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$ sudo docker stop nostalgic_morse
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nostalgic_morse
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We can now use the `docker ps` command to check if the container has
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been stopped.
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$ sudo docker ps -l
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## Restarting our Web Application Container
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Oops! Just after you stopped the container you get a call to say another
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developer needs the container back. From here you have two choices: you
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can create a new container or restart the old one. Let's look at
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starting our previous container back up.
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$ sudo docker start nostalgic_morse
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nostalgic_morse
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Now quickly run `docker ps -l` again to see the running container is
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back up or browse to the container's URL to see if the application
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responds.
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> **Note:**
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> Also available is the `docker restart` command that runs a stop and
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> then start on the container.
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## Removing our Web Application Container
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Your colleague has let you know that they've now finished with the container
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and won't need it again. So let's remove it using the `docker rm` command.
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$ sudo docker rm nostalgic_morse
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Error: Impossible to remove a running container, please stop it first or use -f
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2014/05/24 08:12:56 Error: failed to remove one or more containers
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What's happened? We can't actually remove a running container. This protects
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you from accidentally removing a running container you might need. Let's try
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this again by stopping the container first.
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$ sudo docker stop nostalgic_morse
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nostalgic_morse
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$ sudo docker rm nostalgic_morse
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nostalgic_morse
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And now our container is stopped and deleted.
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> **Note:**
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> Always remember that deleting a container is final!
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# Next steps
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Until now we've only used images that we've downloaded from
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[Docker Hub](https://hub.docker.com) now let's get introduced to
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building and sharing our own images.
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Go to [Working with Docker Images](/userguide/dockerimages).
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