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Merge pull request #150 from pzelnip/codependentcodr/ch264/docker-images-reducing-size
Add post on reducing Docker image sizes [ch264]
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‎Makefile

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@@ -89,7 +89,8 @@ s3_upload:
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docker run -e AWS_ACCESS_KEY_ID=$(AWS_ACCESS_KEY_ID) -e AWS_SECRET_ACCESS_KEY=$(AWS_SECRET_ACCESS_KEY) --rm -it -w /build $(SITE_NAME):latest ./s3_push.sh
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safety:
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docker run -it --rm $(SITE_NAME):latest safety check -r requirements.txt --full-report
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echo "move safety to codependentcodrbase, see https://app.clubhouse.io/codependentcodr/story/265/move-safety-check-to-codependentcodrbase"
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# docker run -it --rm $(SITE_NAME):latest safety check -r requirements.txt --full-report
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bandit:
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docker run -it --rm $(SITE_NAME):latest bandit . -r

‎content/docker-and-image-sizes.md

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Title: Docker and Image Sizes
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Date: 2018-08-11 19:30
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Modified: 2018-08-11 19:30
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Category: Posts
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tags: docker,devops
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cover: static/imgs/default_page_imagev2.jpg
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summary: I was surprised & learned something about building Docker images.
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So this surprised me. I had a Dockerfile that looked basically like this:
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```dockerfile
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FROM alpine:latest
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RUN apk add --no-cache --update \
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python3 nodejs-current-npm make git curl
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RUN python3 -m ensurepip
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RUN pip3 install --upgrade pip
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RUN npm install -g markdownlint-cli
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# needed for one of the packages in requirements.txt
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RUN apk add --no-cache --update python3-dev gcc build-base
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COPY requirements.txt /build/requirements.txt
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RUN pip3 install -r /build/requirements.txt
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```
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Building this image resulted in an image that `docker images` reported as 379MB in
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size. That's a little large so I wanted to trim.
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Since those packages installed just before copying
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`requirements.txt` to the image were only there to be able to *install* a package,
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there's no reason for them to remain in the image. Cool, so we can turf them to
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save on image size:
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```dockerfile
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FROM alpine:latest
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RUN apk add --no-cache --update \
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python3 nodejs-current-npm make git curl
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RUN python3 -m ensurepip
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RUN pip3 install --upgrade pip
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RUN npm install -g markdownlint-cli
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# needed for one of the packages in requirements.txt
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RUN apk add --no-cache --update python3-dev gcc build-base
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COPY requirements.txt /build/requirements.txt
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RUN pip3 install -r /build/requirements.txt
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# cleanup unneeded dependencies
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RUN apk del python3-dev gcc build-base
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```
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Sweet, and this resulted in an image size of *381MB*, a savings of *NEGATIVE 2MB*.
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Wait.... WAT?
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![<INSERT ALT TEXT HERE>]({filename}/static/imgs/wat.jpg)
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So I *removed* some stuff and ended up with an image that's a few MB's *larger*?
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How does that work?
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And this is where if we want to get technical, we start talking about how Docker
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uses a layered filesystem and as such (not entirely unlike Git) once something is
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added to an image, it can't really (or at least easily) be removed.
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See this issue which mentions what I'm talking about:
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<https://github.com/gliderlabs/docker-alpine/issues/45>
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So what do we do? Well, we *combine* the operations into a single Docker instruction:
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```dockerfile
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FROM alpine:latest
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RUN apk add --no-cache --update \
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python3 nodejs-current-npm make git curl
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RUN python3 -m ensurepip
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RUN pip3 install --upgrade pip
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RUN npm install -g markdownlint-cli
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COPY requirements.txt /build/requirements.txt
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RUN apk add --no-cache --update python3-dev gcc build-base && \
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pip3 install -r /build/requirements.txt && \
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apk del python3-dev gcc build-base
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```
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Because the add & the removal of the apk packages are a single Docker instruction
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they don't inflate the size of the built image (you can think of layers as being
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"checkpoints" after each instruction in a `Dockerfile`).
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With this change my image size dropped *significantly*. How much? Let's let the
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tool tell us:
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```shell
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$ docker images
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REPOSITORY TAG IMAGE ID CREATED SIZE
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someimage combineops 1744771da3fa About a minute ago 216MB
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someimage removepckgs fc5877e2afad 4 minutes ago 381MB
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someimage original b6e5e43b22e0 5 minutes ago 379MB
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```
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That is, it dropped from *379MB* to *216MB*. Not a bad savings at all.
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This is a classic "time vs space" tradeoff though. Because I had to move the `requirements.txt`
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line up, that means that builds of this image are often slower (because of the way the Docker
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cache works, if I change the requirements.txt file then it'll have to install those apk packages
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any time `requirements.txt` changes). However, I think the savings in space (40%+) is worth it.

‎content/static/imgs/wat.jpg

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