Wrote out dockerfile cheat sheet

blog/src/docker/dockerfile.md

@@ -1,5 +1,10 @@
 # Dockerfile Cheat Sheet
 
+"Docker can build images automatically by reading the instructions from a `Dockerfile`. A `Dockerfile` is a text document that contains all the commands a user could call on the command line to assemble an image. This page describes the commands you can use in a `Dockerfile`." - Docker Docs
+
+This is meant to be a quick and dirty reference to help you get started. Reference the docker docs if you need more information, they're linked in the sources below.
+
+
 ## Starting Point
 
 Arguments that dictate what to use as a starting point for the dockerfile
@@ -23,25 +28,78 @@ Notes:
 
 Arguments that don't affect how the image builds or container runs, but give information about the image
 
-### MAINTAINER
+### MAINTAINER (DEPRECATED)
 
-Allows you to specify an author
+Allows you to specify an author - REPLACED with `LABEL Author="foo"`
 
 Usage:
 ```
-MAINTAINER <name>
+LABEL Author="<name>"
+# MAINTAINER <name>
+```
+
+### LABEL
+
+Adds metadata to an image
+
+Usage:
+```
+LABEL "com.example.vendor"="ACME Incorporated"
+LABEL com.example.label-with-value="foo"
+LABEL version="1.0"
+LABEL description="This text illustrates \
+that label-values can span multiple lines."
 ```
 
 ## Setup
 
 ### ENV
 
+Specifies environment variables
+Usage:
+```
+ENV <env_var_name> <value>
+```
 
 ### ADD
 
+Copies files or directories to container's file system
+
+Usage:
+```
+# ADD <host_src> <container_dest>
+COPY <host_src> <container_dest>
+```
+Notes:
+- ADD can be buggy, use COPY where you can
+
+### COPY
+
+Copies files or directories to container's file system
+
+Usage:
+```
+COPY <host_src> <container_dest>
+```
+
+### VOLUME
+
+Create mount point, marks as holding external mounted items
+Usage:
+```
+VOLUME ["<DIR_PATH1>", "<DIR_PATH2>", ...]
+```
+
 
 ### WORKDIR
 
+Set the current working directory
+
+Usage:
+```
+WORKDIR <DIR_PATH>
+```
+
 ### SHELL
 
 Command to change the shell that RUN uses
@@ -72,8 +130,6 @@ Notes:
 
 
 
-### CMD
-
 
 ### 
 
@@ -81,5 +137,45 @@ Notes:
 
 ### EXPOSE
 
+A way of communicating/documenting which image ports should be forwarded when ran as a container
+
+```
+EXPOSE 80
+# ^ notes that tcp port 80 should be opened
+EXPOSE 53/udp
+# ^ Specifies udp on port 53
+EXPOSE 53/tcp
+EXPOSE 53/udp
+# ^ Specifies both udp and tcp
+```
+Notes:
+- Doesn't actually open the port, you'll need to add that to the docker-compose file or docker run (-p) command
 
 
+### CMD
+
+Marks the command to be run automatically when a container starts if none is manually marked at runtime
+
+Usage:
+```
+CMD ["<executable>", "<arg1>", "<arg2>"]
+CMD ["<arg1>", "<arg2>"]
+CMD <command> <arg1> <arg2>
+```
+Notes:
+- If you are also using ENTRYPOINT, you can use CMD to specify arguments only
+
+### ENTRYPOINT
+
+Marks the command to be run automatically when a container is run interactively, overrides CMD 
+Usage:
+```
+ENTRYPOINT ["<executable>", "<arg1>", "<arg2>"]
+ENTRYPOINT <command> <arg1> <arg2>
+```
+# Sources
+
+- [docs.docker.com](https://docs.docker.com/engine/reference/builder/)
+- [kapeli.com](https://kapeli.com/cheat_sheets/Dockerfile.docset/Contents/Resources/Documents/index)
+- [dockerlaps.collabnix.com](https://dockerlabs.collabnix.com/docker/cheatsheet/)
+