Dockerfile - kimschles/schlesinger-knowledge GitHub Wiki

Dockerfile Gotchas

FROM

• Sets the base image for the rest of the Dockerfile instructions
• Sets up the envioronment: node.js, ruby, java, etc.

COPY

• The COPY instruction copies new files or directories from and adds them to the filesystem of the container at the path .
• copy directories or files from the source and add them to the destination container's filesystem
• COPY <src> <dest>
• COPY say_hello.sh /mydir/
• The original version

ADD

• The ADD instruction copies new files, directories or remote file URLs from and adds them to the filesystem of the image at the path .
• ADD lets you copy directories, files or files from URLS from the source and adds them to the filesystem of an image
• ADD lets you add local files to your docker image
  • Local to what? Local directory
• The updated version

ADD say_hello.sh /

• Makes a copy of the file you're specifiying in the root director of the filesystem

COPY vs. ADD *

CMD

• CMD allows you to treat your docker container like an executable binary
• If you only use

ENTRYPOINT

• An ENTRYPOINT allows you to configure a container that will run as an executable.
• Allows you to id which executable should be run when a container is started from your image
• Used more often
• The default command that gets run

CMD vs. ENTRYPOINT

• You can manually override CMD with docker run
• Entrypoint will overrider commands with docker run

RUN

• create a new container, start it and run a process in it
• this command will run the commands in a new layer on top of the current image and commit the results

EXEC

• when you want to run a command in an existing container

RUN vs EXEC

• Docker Run vs. Exec

EXPOSE

• The port on which the container listens for connetions
• Apache Web Server: EXPOSE 80
• MongoDB: EXPOSE 27017

IP Address is like an address A port is like a mailbox in an apartment building

Like a telephone switchboard. A port is like the jack.

ARG

• Allows the developer to set values during the docker build process

HEALTHCHECK

• A way to check if a running container is healthy