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BlogTL;DR
Starting from Docker 17.05+, you can create a single Dockerfile that can build multiple helper images with compilers, tools, and tests and use files from above images to produce the final Docker image. Read this simple tutorial and create a free Codefresh account to build, test and deploy images instantly.
The “core principle” of Dockerfile
Docker can build images by reading the instructions from a Dockerfile. A Dockerfile is a text file that contains a list of all the commands needed to build a new Docker image. The syntax of Dockerfile is pretty simple and the Docker team tries to keep it intact between Docker engine releases.
The core principle is very simple: 1 Dockerfile -> 1 Docker Image.
This principle works just fine for basic use cases, where you just need to demonstrate Docker capabilities or put some “static” content into a Docker image.
Once you advance with Docker and would like to create secure and lean Docker images, a single Dockerfile is not enough.
People who insist on following the above principle find themselves with slow Docker builds, huge Docker images (several GB size images), slow deployment time and lots of CVE violations embedded into these images.
The Docker Build Container pattern
Docker Pattern: The Build Container
The basic idea behind Build Container pattern is simple:
Create additional Docker images with required tools (compilers, linters, testing tools) and use these images to produce lean, secure and production ready Docker image.
An example of the Build Container pattern for typical Node.js application:
- Derive
FROMa Node base image (for examplenode:6.10-alpine)nodeandnpminstalled (Dockerfile.build) - Add
package.json - Install all node modules from
dependencyanddevDependency - Copy application code
- Run compilers, code coverage, linters, code analysis and testing tools
- Create the production Docker image; derive
FROMsame or other Node base image - install node modules required for runtime (
npm install --only=production) - expose
PORTand define a defaultCMD(command to run your application) - Push the production image to some Docker registry
This flow assumes that you are using two or more Dockerfiles and a shell script or flow tool to orchestrate all steps above.
Example
I use a fork of Let’s Chat node.js application. Here is the link to our fork.
Builder Docker image with eslint, mocha and gulp
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FROM alpine:3.5 # install node RUN apk add --no-cache nodejs # set working directory WORKDIR /root/chat # copy project file COPY package.json . # install node packages RUN npm set progress=false && \ npm config set depth 0 && \ npm install # copy app files COPY . . # run linter, setup and tests CMD npm run lint && npm run setup && npm run test |
Production Docker image with ‘production’ node modules only
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FROM alpine:3.5 # install node RUN apk add –no-cache nodejs tini # set working directory WORKDIR /root/chat # copy project file COPY package.json . # install node packages RUN npm set progress=false && \ npm config set depth 0 && \ npm install --only=production && \ npm cache clean # copy app files COPY . . # Set tini as entrypoint ENTRYPOINT [“/sbin/tini”, “--”] # application server port EXPOSE 5000 # default run command CMD npm run start |
What is Docker multi-stage build?
Docker 17.05 extends Dockerfile syntax to support new multi-stage build, by extending two commands: FROM and COPY.
The multi-stage build allows using multiple FROM commands in the same Dockerfile. The last FROM command produces the final Docker image, all other images are intermediate images (no final Docker image is produced, but all layers are cached).
The FROM syntax also supports AS keyword. Use AS keyword to give the current image a logical name and reference to it later by this name.
To copy files from intermediate images use COPY --from=<image_AS_name|image_number>, where number starts from 0 (but better to use logical name through AS keyword).
Creating a multi-stage Dockerfile for Node.js application
The Dockerfile below makes the Build Container pattern obsolete, allowing to achieve the same result with the single file.
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# # ---- Base Node ---- FROM alpine:3.5 AS base # install node RUN apk add --no-cache nodejs-current tini # set working directory WORKDIR /root/chat # Set tini as entrypoint ENTRYPOINT ["/sbin/tini", "--"] # copy project file COPY package.json . # # ---- Dependencies ---- FROM base AS dependencies # install node packages RUN npm set progress=false && npm config set depth 0 RUN npm install --only=production # copy production node_modules aside RUN cp -R node_modules prod_node_modules # install ALL node_modules, including 'devDependencies' RUN npm install # # ---- Test ---- # run linters, setup and tests FROM dependencies AS test COPY . . RUN npm run lint && npm run setup && npm run test # # ---- Release ---- FROM base AS release # copy production node_modules COPY --from=dependencies /root/chat/prod_node_modules ./node_modules # copy app sources COPY . . # expose port and define CMD EXPOSE 5000 CMD npm run start |
The above Dockerfile creates 3 intermediate Docker images and single release Docker image (the final FROM).
- First image
FROM alpine:3.5 AS bas– is a base Node image with:node,npm,tini(init app) andpackage.json - Second image
FROM base AS dependencies– contains all node modules fromdependenciesanddevDependencieswith additional copy ofdependenciesrequired for final image only - Third image
FROM dependencies AS test– runs linters, setup and tests (withmocha); if this run command fail not final image is produced - The final image
FROM base AS release– is a base Node image with application code and all node modules fromdependencies
Try Docker multi-stage build today
In order to try Docker multi-stage build, you need to get Docker 17.05, which is going to be released in May and currently available on the beta channel.
So, you have two options:
- Use beta channel to get Docker 17.05
- Run dind container (docker-in-docker)
Running Docker-in-Docker 17.05 (beta)
Running Docker 17.05 (beta) in docker container (--privileged is required):
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$ docker run -d --rm --privileged -p 23751:2375 --name dind \ docker:17.05.0-ce-dind --storage-driver overlay2 |
Try mult-stage build. Add --host=:23751 to every Docker command, or set DOCKER_HOST environment variable.
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$ # using --host $ docker --host=:23751 build -t local/chat:multi-stage . $ # OR: setting DOCKER_HOST $ export DOCKER_HOST=localhost:23751 $ docker build -t local/chat:multi-stage . |
Summary
With Docker multi-stage build feature, it’s possible to implement an advanced Docker image build pipeline using a single Dockerfile .
Kudos to Docker team for such a useful feature!
Hope, you find this post useful. I look forward to your comments and any questions you have.
PS Codefresh just added multi-stage build support, Please go on and create a free Codefresh account to try this out.
Dan Garfield
Cheers, good explanation and clean Dockerfile!
Thx for the blog. However, the build process failed…
npm ERR! Linux 3.13.0-91-generic
npm ERR! argv “/usr/bin/node” “/usr/bin/npm” “run” “lint”
npm ERR! node v6.9.2
npm ERR! npm v3.10.9
npm ERR! missing script: lint
npm ERR!
npm ERR! If you need help, you may report this error at:
npm ERR!
npm ERR! Please include the following file with any support request:
npm ERR! /root/chat/npm-debug.log
I was thinking there was a way to build only one stage. But it looks like Docker will go through all stages, only the last stage in the Dockerfile is the what will be assigned as the image?
This doesn’t help if I want i want to end on an earlier stage. Such as if I have a dev stage, is there anyway to start the container in that stage?
You can always create a new Docker container from any LAYER. Just run
docker historycommand to see all image layers. Then select some layer, for exampleb3616e272dc1and run it as a container:$ docker run -it --rm b3616e272dc1 shif you like to keep specific layer for future use, tag it:
$ docker tag b3616e272dc1 myrepo/myimage:masterThis is great! NowI would like to mix this with pkg (https://github.com/zeit/pkg)
I think that would be the ultimate NodeApp deployment setup 🙂
Interesting article. Would I be correct in saying this mirrors a CI build pipeline?
Correction: The docker version required for this is 17.05+, not 17.0.5+. That erroneous extra decimal point makes a difference
Thanks Jay, fixed!
What is the difference between executing npm install in an intermediate container, then copy it in the final one vs. Just executing npm install in the final container?
Speed.
Why downloading
npmpackages twice? For a small project it makes no difference, but for real project, it can take minutes (depends on network latency).I’d love to see an extended example of this with a compose file – any chance?
Thanks!
This will work only if you configure your lint, setup and test as production dependencies, right?
The basic idea is to have 2 folders in
baseimage: one withproductiondependencies and other withdev.Then
testintermediate image could use (copy)devdependencies frombaseandreleaseimage will copy onlyproductiondependencies.If
testintermediate image fails some test or lint rule, finalreleaseimage won’t be built.Fantastic Post! Thank you so much for sharing this kind of wonderful post..!!
Cool feature!
If the dockerfile step for say linting fails, would it stop it from progressing to the next chain?
Any failed command (one that exits with non-zero code) will stop the Docker build
Btw:
RUN npm install –only=production
copy production node_modules aside
RUN cp -R node_modules prod_node_modules
That’s smart!
Your article is very nice… thanks for shairng your information….
Hello,
Is it possible to launch only a specific stage in the docker-compose file ?
I want to run unit tests separately when I want to,
for example:
i want to report tests in jenkinsfile in a specific file, as report.xml and I want to launch
thx
A couple of observations:
I haven’t seen any solution that isn’t running sequentially. We run NPM Lint, NPM tests, image build, … all in parallel to maximise speed.
Caching of NPM modules across multiple CI runs – How is this working?
For caching between CI builds, we (in Codefresh) are using high-iops network volumes mounted into
buildercontainer, so subsequent builds, even if running on different machines will reuse the same volume (ot it’s clone, depending on load and git branching).