Docker Cookbook

44 | Chapter 2: Image Creation and Sharing

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This creates a 
flask
Docker image:
$ docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
flask latest d381310506ed 4 days ago 354.6 MB
cookbook echo e778362ca7cf 4 days ago 192.7 MB
ubuntu 14.04 9bd07e480c5b 10 days ago 192.7 MB
To run the application, you use the 
-d
option of 
docker run
, which daemonizes the
container, and you also use the 
-P
option of 
docker run
to let Docker choose a port
on the Docker host that will be mapped to the exposed port specified in the Docker‐
file (e.g., 5000):
$ docker run -d -P flask
5ac72ed12a72f0e2bec0001b3e78f11660905d20f40e670d42aee292263cb890
$ docker ps
CONTAINER ID IMAGE COMMAND ... PORTS
5ac72ed12a72 flask:latest "python /tmp/hello.p ... 0.0.0.0:49153->5000/tcp
The container returns, it is daemonized, and you are not logged in to an interactive
shell. 
PORTS
shows a mapping between port 5000 of the container and port 49153 of
the Docker host. A simple 
curl
 to 
http://localhost:49153/hi
returns 
Hello World
, or
you can open your browser to the same URL.
If you are using Boot2Docker, you will have to use the IP address of
the bridge network, instead of 
localhost
. If you do want to use
localhost
, add port forwarding rules in VirtualBox.
Discussion
Since your Dockerfile specified a command to run via 
CMD
, you do not need to specify
a command after the name of the image to use. However, you can override this com‐
mand and start the container in interactive mode by starting a bash shell like so:
$ docker run -t -i -P flask /bin/bash
root@fc1514ced93e:/# ls -l /tmp
total 4
-rw-r--r-- 1 root root 194 Dec 8 13:41 hello.py
root@fc1514ced93e:/#