29 Jul 2015, 13:28

Building a docker image from scratch

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Building a docker image from scratch

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This post assumes that you have a working docker environment already set up.

Here are the really simple instructions:

  1. create a Dockerfile
  2. open the Dockerfile
  3. add a FROM statement with a base image
  4. add a RUN statement for running whatever setup commands are needed
  5. add any additional RUN statements necessary
  6. add a COPY statement for copying stuff over from the local filesystem
  7. run docker build -t user/image_name:v1 .
  8. run docker run user/image_name:v1

Dockerfile

testfile

The following is the contents of testfile:

this is a test file

As you’re writing your Dockerfile, it may be helpful to run the commands against a real image as you go, so that you can more easily predict what’s happening. Here is how to do that:

docker pull debian:latest
docker run -t -i debian:latest /bin/bash

If you want to generate a docker image based off of what you did in the interactive session vs a Dockerfile, you can take note of the image id in the console after root. E.g. root@28934273 # specifies the user is root and the image id is 28934273. Then, you can run whatever commands you’d like, exit the session, and run the following:

docker commit -m "ran some commands" -a "My Name" \
28934273 user/debian:v1

  • -m is the commit message
  • -a is the author’s name

Now, you can run that image:

docker run -t -i user/debian:v1

You can use the image you just created as a base image in another of your Dockerfiles, so that you can interactively set up your image initially, and then in the second step, add any CMD statements to actually run your software.

Refernces

Documentation pulled from:

Code

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