change headlines and slugs

Author: kapnobatai137

docker/fundamentals/images/dockerfile-ii.md .archived/docker/fundamentals/images/dockerfile-ii.md

@@ -4,7 +4,7 @@ description: Docker container blueprints
 
 insights:
   - docker-images
-  - dockerfile
-  - dockerfile-ii
+  - dockerfile-format
+  - dockerfile-instructions
   - docker-image-tags
   - docker-image-registries

docker/fundamentals/images/dockerfile.md .archived/docker/fundamentals/images/dockerfile.md

@@ -0,0 +1,107 @@
+---
+author: nem035
+aspects:
+  - introduction
+  - workout
+type: normal
+category: must-know
+links:
+- '[Best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/){article}'
+- '[Dockerfile reference](https://docs.docker.com/engine/reference/builder/){documentation}'
+---
+
+# Dockerfile Format
+
+---
+
+## Content
+
+A Dockerfile represents an image creation spec.
+
+Essentially, it is just a text file with Docker-specific syntax that contains all the instructions the Docker daemon can use to build a specific image.
+
+Instructions in a Dockerfile are executed in order, top-down.
+
+The format of a Dockerfile is the following:
+
+```Dockerfile
+# Comment
+INSTRUCTION arguments
+```
+
+Dockerfile instructions are UPPERCASE by convention to more easily distinguish them from their arguments.
+
+Here's an example of a Dockerfile:
+
+```Dockerfile
+# Use the node image as the base image
+FROM node
+
+# Initialize an env var for this image
+# that has a default value of "fun"
+ENV ENKI="fun"
+
+# the RUN command allows us to run any
+# shell command or bash script available
+# at this step of building the image.
+# This command will have access to all
+# environment variables created above it.
+RUN echo "Learning Docker is $ENKI"
+
+# Expose port 1234 on the container.
+# We still have to use -p when running this
+# container to link this port to an exposed
+# port on the host in which the container is
+# running
+EXPOSE 1234
+
+# CMD (and/or ENTRYPOINT) is a required
+# command. It is a final command that will
+# be run every time a container is launched
+# (or restarted). Only one CMD is allowed.
+# If there are multiple, last one wins.
+CMD ["echo", "Docker", "is", "cool"]
+```
+
+To build an image from a Dockerfile within the `enki` directory, we would do:
+
+```bash
+docker build enki
+```
+
+Here's an example output of building an image from the Dockerfile above:
+
+Sending build context to Docker daemon  23.29MB
+Step 1/5 : FROM node
+latest: Pulling from library/node
+9cc2ad81d40d: Pull complete
+e6cb98e32a52: Pull complete
+ae1b8d879bad: Pull complete
+42cfa3699b05: Pull complete
+053cac798c4e: Pull complete
+e11ff976ff71: Pull complete
+6e754155fada: Pull complete
+32d7c2fdf415: Pull complete
+7acfea3f0d48: Pull complete
+Digest: sha256:xxx
+Status: Downloaded newer image for node:latest
+ ---> b18afbdfc458
+Step 2/5 : ENV ENKI="fun"
+ ---> Running in 3560df900d1f
+Removing intermediate container 3560df900d1f
+ ---> 53a94ebce927
+Step 3/5 : RUN echo "Learning Docker is $ENKI"
+ ---> Running in e42c0617e98e
+Learning Docker is fun
+Removing intermediate container e42c0617e98e
+ ---> 78a48477a76d
+Step 4/5 : EXPOSE 1234
+ ---> Running in a1df0ebf5605
+Removing intermediate container a1df0ebf5605
+ ---> 15a139f293da
+Step 5/5 : CMD ["echo", "Docker", "is", "cool"]
+ ---> Running in 3c8e7b309484
+Removing intermediate container 3c8e7b309484
+ ---> 8c40e5b0c9b9
+Successfully built 8c40e5b0c9b9
+```

docker/fundamentals/images/README.md

@@ -0,0 +1,62 @@
+---
+author: nem035
+aspects:
+  - introduction
+  - workout
+type: normal
+category: must-know
+links:
+- '[Best practices for writing Dockerfiles](https://docs.docker.com/develop/develop-images/dockerfile_best-practices/){article}'
+- '[Dockerfile reference](https://docs.docker.com/engine/reference/builder/){documentation}'
+---
+
+# Dockerfile Instructions
+
+---
+
+## Content
+
+A Dockerfile must start with a `FROM` instruction which initializes a new build stage and sets the base image for subsequent instructions.
+
+`FROM` may only be preceded by one or more `ARG` instructions, which represent externally passed build arguments into the image building process.
+
+```bash
+docker build . \
+  --build-arg EXAMPLE="this is an"
+```
+
+A Dockerfile must contain at least the `CMD` or the `ENTRYPOINT` instruction to indicate the start command for an image.
+
+The `RUN` instruction executes the commands in a new layer on top of the current image. Each successive `RUN` instruction builds a new image layer on top of the previous one.
+
+Each Dockerfile instruction result gets cached.
+
+When evaluating each instruction, Docker will look for an existing image in its cache that it can reuse, rather than creating a new (duplicate) image.
+
+This is why re-building an image is faster than the initial build because we can re-use the cached layers.
+
+Whenever we change a line in the Dockerfile, the cached result for every line after it is invalidated and has to be re-computed.
+
+Due to this, a good convention is to keep the things that change the least at the top of the Dockerfile and things that change the most at the bottom.
+
+---
+
+## Practice
+
+A Dockerfile contains instructions the Docker daemon uses to build containers.
+
+???
+
+* false
+* true
+
+---
+
+## Revision
+
+The result of each Dockerfile instruction is cached and dependent on the cached result of the instruction before it.
+
+???
+
+* true
+* false