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Docker_Notes.md

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Helpful links

You MUST go through https://docs.docker.com/engine/reference/builder/ and https://docs.docker.com/engine/reference/run/ at least twice!
https://serversforhackers.com/getting-started-with-docker
http://rominirani.com/2015/07/19/docker-tutorial-series/

Terminology

Container
Like a hardware unit - analogous to your laptop, for e.g.
A container is a stripped-to-basics version of a Linux operating system.

Image
Analogous to the OS that will run on your laptop (on the container)
An image is software you load into a container.

Errors

  1. nik kvs$ sudo docker build -t nkini/kvs .
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/binary-amd64/Packages  Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.

    Solution:
    Made the error go away by commenting the following line in the Docker file
    RUN apt-get update && apt-get install -y python3
    However, I did not ever see the error again after that, even with the line above uncommented.

  2. Dockerfile:    
.  
.  
CMD ["cd","/root/webapp"]  
CMD ["python3", "-m", "http.server"]  
.  
.

    The result of

    nik kvs$ curl -i localhost:49160

    shows that httpserver is running at / and NOT at /root/webapp.

    Solution:
    This just means that I haven't read the docs. https://docs.docker.com/engine/reference/builder/#cmd
    "There can only be one CMD instruction in a Dockerfile. If you list more than one CMD then only the last CMD will take effect."
    Write multiple shell commands as

    CMD     cd /root/webapp; python3 app.py

    or better still, put them in a shell script file and run the script.

  3. nik kvs$ cat Dockerfile 
.
.
.
RUN cd /root/webapp; python3 -m http.server;

nik kvs$ sudo docker build -t nkini/kvs .
.
.
.
Removing intermediate container e6d7aca4930a
Step 5 : RUN cd /root/webapp; python3 -m http.server
 ---> Running in 4a1079fd7173
 #JUST HANGS HERE

    Solution:
    I can't quite put a finger on exactly why, but you can't have your last command in the Dockerfile be a RUN like the one here. It needs to be a CMD.

    .
.
.
CMD cd /root/webapp; python3 -m http.server;

    Do read https://docs.docker.com/engine/reference/builder/#run and https://docs.docker.com/engine/reference/builder/#cmd once more.

  4. nik kvs$ sudo docker run -d -p 49160:8080 nkini/kvs
nik kvs$ curl -i localhost:49160
curl: (56) Recv failure: Connection reset by peer

    Solution:
    If your app 127.0.0.1 or 0.0.0.0? Changing the host of the app running in the Docker container to 0.0.0.0 (from what was initially 127.0.0.1) fixed this error for me.