New Section: Dockerfile ENTRYPOINT and CMD

dockerfiles/README.md

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+# Dockerfile Next Steps 
+Table of Contents
+
+[Understanding ENTRYPOINT and CMD](#entrypoint-and-cmd)
+
+## Understanding ENTRYPOINT and CMD
+
+### What's an ENTRYPOINT? What's a CMD? 
+
+#### ENTRYPOINT 
+
+An `ENTRYPOINT` allows you to configure a container that will run as an executable. 
+
+There are _two_ forms: the _exec form_ and the _shell form_.
+
+__SYNTAX__
+
+```Dockerfile
+ENTRYPOINT ["executable", "param1", "param2"] # execform
+```    
+
+```Dockerfile
+ENTRYPOINT command param1 param2 # shellform
+```
+
+When you run a container, any command line arguments will be appended to the entrypoint.
+
+This feature allows us to create images with a default executable in mind or change the default entrypoint of a base image.
+
+For example, the default entrypoint for the offical nginx image is `ENTRYPOINT ["/docker-entrypoint.sh"]` [1](https://github.com/nginxinc/docker-nginx/blob/2decc81a019b5df087c9162d3621b1c9beb3104f/mainline/debian/Dockerfile). We can override this to print the contents of the container filesystem instead.
+
+```Dockerfile
+FROM nginx:1.21.4
+ENTRYPOINT ["ls"]
+```
+#### CMD 
+
+`CMD` provides defaults for an executing container. These defaults can include an executable, or they can omit the executable, in which case the executable is the entrypoint.
+
+There are _three_ forms:
+
+__SYNTAX__
+
+```Dockerfile
+CMD ["executable","param1","param2"] # execform
+```
+
+```Dockerfile
+CMD ["param1","param2"] # parameter-only form 
+```
+
+```Dockerfile
+CMD command param1 param2 # shellform 
+```
+
+__NOTE:__ If you omit the executable, you must have an ENTRYPOINT defined in the Dockerfile. 
+
+Using the same custom nginx image, this is how it would look like using CMD.
+
+```dockerfile
+FROM nginx:1.21.4
+CMD ["ls"]
+```
+Now you might be wondering, if we can use CMD in the same way as ENTRYPOINT why does Docker need both? The truth is, they compliment each other. ENTRYPOINT and CMD are often used together. When a command is present, it's appended to the end of the entrypoint.
+
+For example:
+
+```dockerfile
+FROM nginx:1.21.4
+ENTRYPOINT ["ls"]
+CMD ["-l"]
+# becomes "ls -l"
+```
+
+#### Summary
+
+Both ENTRYPOINT and CMD provide increased flexibility in how we write Dockerfiles. They allow us to provide good defaults in our images, with the option to change this behavior at runtime.
+
+### Lecture 1: ENTRYPOINT
+
+In this lecture, we will discuss ENTRYPOINT.
+
+### Exercise
+
+In this exercise...
+
+Exercise Files
+
+- [/dockerfiles/entrypoint-1](/dockerfiles/entrypoint-1)
+
+Resources
+
+- https://docs.docker.com/engine/reference/builder/#entrypoint
+
+### Lecture 2: CMD
+
+In this lecture, we will discuss CMD.
+
+### Exercise
+
+In this exercise...
+
+Exercise Files
+
+- [/dockerfiles/command-1](/dockerfiles/command-1)
+
+Resources
+
+- https://docs.docker.com/engine/reference/builder/#cmd
+
+### Lecture 3: OVERRIDING ENTRYPOINT and CMD in the CLI
+
+In this lecture, we will discuss command line properties.
+
+```
+--entrypoint		Overwrite the default ENTRYPOINT of the image
+```
+
+You can overwrite the command at the command line as well.
+
+### Exercise
+
+In this exercise...
+
+Exercise Files
+
+- [/dockerfiles/entrypoint-2](/dockerfiles/entrypoint-2)
+- [/dockerfiles/command-2](/dockerfiles/command-2)
+
+Resources
+- https://docs.docker.com/engine/reference/commandline/run/#options (--entrypoint)
+
+
+### Lecture 4: Using ENTRYPOINT and CMD in Docker Compose
+
+In this lecture, we will discuss compose properties.
+
+```
+entrypoint: ["php", "-d", "memory_limit=-1", "vendor/bin/phpunit"]
+```
+
+```
+command: ["bundle", "exec", "thin", "-p", "3000"]
+```
+
+### Exercise
+
+In this exercise...
+
+Exercise Files
+
+- [/dockerfiles/entrypoint-3](/dockerfiles/entrypoint-3)
+- [/dockerfiles/command-3](/dockerfiles/command-3)
+
+Resources
+- https://docs.docker.com/compose/compose-file/compose-file-v3/#entrypoint
+- https://docs.docker.com/compose/compose-file/compose-file-v3/#command
+
+
+<hr/>
+
+<details>
+<summary>Quiz</summary>
+
+<br/>
+
+1. When would you want to use both a command and entrypoint?
+
+    A)
+
+    B)
+
+    C) 
+
+    D) 
+
+2. Which of the following statements are true?
+
+    A)
+
+    B)
+
+    C) 
+
+    D) 
+
+3. Select the correct way to do X?
+
+    A)
+
+    B)
+
+    C) 
+
+    D) 
+
+<br>
+
+<details>
+<summary>See Quiz Answers</summary>
+<br>
+
+- Q1: __A__
+- Q2: __C__
+- Q3: __D__
+</details>
+</details>
+<hr/>
+
+### Assignment 1: Build a curl image
+
+For this assignment, your task is to...
+
+Assignment Files
+
+[/dockerfiles/entrypoint-command-assignment-1](/dockerfiles/entrypoint-cmd-assignment-1)