Debugging a Dockerfile

Sometimes creating a Dockerfile may not start with everything working. A Dockerfile does not always build images and sometimes it does, but starting a container would crash on startup.

Every instruction we set in the Dockerfile is going to be built as a separate, temporary image for the other instruction to build itself on top of the previous instruction. The following example explains this:

1. Create a Dockerfile using your favorite editor:

      FROM busybox 
      RUN ls -lh 
      CMD echo Hello world 

2. Now, build the image by executing the following command:

      $ docker build .
      Sending build context to Docker daemon 2.048 kB
      Step 1 : FROM busybox
      latest: Pulling from library/busybox
      56bec22e3559: Pull complete 
      Digest: sha256:29f5d56d12684887bdfa50dcd29fc31eea4aaf4ad3bec43daf19026a7ce69912
      Status: Downloaded newer image for busybox:latest
      ---> e02e811dd08f
      Step 2 : RUN ls -lh
      ---> Running in 7b47d3c46cfa
 ...