DCEU 18: Developing with Docker Containers

@rhein_wein
Director of Engineering
CloudBees
Laura Frank Tacho

1 DOCKER COMPOSE BASICS
2 OPTIMIZING IMAGES
3 DEBUGGING IN CONTAINERS

Developer Tools
• Docker Compose
• Docker Desktop
• Docker for Mac
• Docker for Windows
• Easiest way to run Docker and Kubernetes on your local
machine
https://www.docker.com/products/docker-desktop

Sample App: Cats vs Dogs
vote result
github.com/rheinwein/example-voting-app

worker
.NET
vote
python
redis
redis
db
postgres
result
node-js

Use from DockerHub
Develop, build, and test
worker
.NET
vote
python
redis
redis
db
postgres
result
node-js

DCEU 18: Developing with Docker Containers

What Happened?
example-voting-app $ docker-compose ps
Name Command State Ports
-------------------------------------------------------------------------------------------------------------------
db docker-entrypoint.sh postgres Up 5432/tcp
example-voting-app_result_1 nodemon --inspect=[::]:585 ... Up 0.0.0.0:5858->5858/tcp, 0.0.0.0:5001->80/tcp
example-voting-app_vote_1 python app.py Up 0.0.0.0:5000->80/tcp
example-voting-app_worker_1 /bin/sh -c dotnet src/Work ... Up
redis docker-entrypoint.sh redis ... Up 0.0.0.0:32774->6379/tcp
example-voting-app $ docker ps # filtering output
CONTAINER ID IMAGE COMMAND STATUS PORTS
7852e34c057f example-voting-app_worker "/bin/sh -c 'dotnet …" Up 6 minutes
3bca5cc2eb09 postgres:9.4 "docker-entrypoint.s…" Up 6 minutes 5432/tcp
b0d3c9cd007c example-voting-app_vote "python app.py” Up 6 minutes 0.0.0.0:5000->80/tcp
9702bb12b70b redis:alpine "docker-entrypoint.s…" Up 6 minutes 0.0.0.0:32774->6379/tcp
072da9ac67e3 example-voting-app_result "nodemon --inspect=[…" Up 6 minutes 0.0.0.0:5858->5858/tcp

What Happened?
example-voting-app $ docker-compose ps
Name Command State Ports
-------------------------------------------------------------------------------------------------------------------
example-voting-app_result_1 nodemon --inspect=[::]:585 ... Up 0.0.0.0:5858->5858/tcp, 0.0.0.0:5001->80/tcp
example-voting-app_vote_1 python app.py Up 0.0.0.0:5000->80/tcp
example-voting-app_worker_1 /bin/sh -c dotnet src/Work ... Up
redis docker-entrypoint.sh redis ... Up 0.0.0.0:32774->6379/tcp
example-voting-app $ docker ps # filtering output
CONTAINER ID IMAGE COMMAND STATUS PORTS
7852e34c057f example-voting-app_worker "/bin/sh -c 'dotnet …" Up 6 minutes
b0d3c9cd007c example-voting-app_vote "python app.py” Up 6 minutes 0.0.0.0:5000->80/tcp
9702bb12b70b redis:alpine "docker-entrypoint.s…" Up 6 minutes 0.0.0.0:32774->6379/tcp
072da9ac67e3 example-voting-app_result "nodemon --inspect=[…" Up 6 minutes 0.0.0.0:5858->5858/tcp

Text Editor
Container
Browser
Source Code
Access local code
See changes in the
browser immediately

Accessing Local Code
version: "3"
services:
result:
build: ./result
command: nodemon server.js
volumes:
- ./result:/app
ports:
- "5001:80"
- "5858:5858"
networks:
- front-tier
- back-tier
Runtime vs Buildtime
This will overwrite the code
copied into the image at
buildtime. Now you’re able to
edit local code and have those
changes reflected in the
container
docker-compose.yml

version: "3"
services:
redis:
image: redis:alpine
container_name: redis
ports:
- "6379"
networks:
- back-tier
def get_redis():
if not hasattr(g, 'redis'):
g.redis = Redis(host="redis", db=0, socket_timeout=5)
return g.redis
vote/app.pydocker-compose.yml
Managing External Dependencies

You don’t need to run your
database in a container.

‣ If you store application data in the
container, that data is lost when the
container is stopped and removed
‣ Using volumes allows data to persist
beyond the lifecycle of the container
‣ Drivers are available for cloud services
‣ You can also use your local disk
Data Volumes
services:
...
db:
image: postgres:9.4
container_name: db
volumes:
- "db-data:/var/lib/postgresql/data"
networks:
- back-tier
volumes:
db-data:
docker-compose.yml

Dockerfiles and container
images are the heart of your
application.
Everything else in the container
ecosystem assumes that you have
your source code available as a
container time.

FROM node:10.9-alpine
RUN mkdir -p /app
WORKDIR /app
RUN npm install -g nodemon
RUN npm config set registry https://
registry.npmjs.org
COPY package.json /app/package.json
RUN npm install
&& npm ls
&& npm cache clean --force
&& mv /app/node_modules /node_modules
COPY . /app
ENV PORT 80
EXPOSE 80
CMD ["node", "server.js"]
A Dockerfile a list of instructions
outlining packages, files,
dependencies, and everything required
for your application to run.
result/Dockerfile

FROM node:10.9-alpine
RUN mkdir -p /app
WORKDIR /app
RUN npm install -g nodemon
RUN npm config set registry https://
registry.npmjs.org
RUN npm install
&& npm ls
COPY . /app
ENV PORT 80
EXPOSE 80
CMD ["node", "server.js"]
Depending on your language, select a
suitable base image and then install the
packages and run setup commands
necessary for your application.
In general, aim to have as small of an
image as possible, but you can always
optimize later.
result/Dockerfile

For faster dev cycles, optimize
your images.

If nothing changes in a layer command, Docker
will use an existing version.
At buildtime, these cache hits can drastically
reduce the time to build and push your image.
Cache misses will add extra time, and you can
optimize your image to avoid them during
development.
Use Caching Effectively

Order Layers for Better Cache Usage
Copy over package or dependency manifests and install those before copying the
rest of the code. Lockfiles change infrequently, so it’s not necessary to reinstall
everything all the time.
RUN npm install
&& npm ls
COPY . /app

Dockerfile Best Practices with Tibor and Sebastiaan
Watch the recording when it’s available!

Pick Base Images Wisely!
By now, almost every major language
or framework maintains a slim version
of their library image, tagged with slim
or specifically with alpine.
Warning: the size of an image on
Docker Hub is the compressed size.
hub.docker.com/_/node

Avoid Anti-Patterns
‣ Simultaneous Innovation
‣ Skipping the fundamentals like giving love to your Dockerfiles
‣ Forgetting other development best practices like pinning dependencies to
versions — this stuff still matters even if you’re using containers
‣ For example, don’t use the latest tag

You can access log output either via Docker Compose or Docker directly.
$ docker-compose logs # this returns all logs for all services
db | LOG: stats_timestamp 2018-09-12 10:35:03.286676+00 is later than collector's time
2018-09-12 10:35:03.262932+00 for database 12141
result_1 | [nodemon] restarting due to changes...
result_1 | [nodemon] starting `node --inspect=[::]:5858 server.js`
result_1 | Debugger listening on ws://[::]:5858/f6dd534f-1976-421c-b4e2-8d3b1baf2622
result_1 | For help, see: https://nodejs.org/en/docs/inspector
result_1 | App running on port 80
result_1 | Connected to db
result_1 | Debugger attached.
redis | 1:M 12 Sep 08:33:52.991 # WARNING: The TCP backlog setting of 511 cannot be enforced
because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis | 1:M 12 Sep 08:33:52.991 # Server initialized
Viewing Log Output

Viewing Log Output
Logs are visible by default when starting your app with docker-compose up. If you prefer
a tidy terminal, use up with the -d flag. You can get logs per service later.
Tip: timestamps are available with a flag.
$ docker-compose up -d
...
$ docker-compose logs -t worker # docker logs -t example-voting-app_worker_1
worker_1 | 2018-09-12T08:22:49.367373200Z Waiting for db
worker_1 | 2018-09-12T08:22:50.371369500Z Waiting for db
worker_1 | 2018-09-12T08:22:53.526120800Z Connected to db
worker_1 | 2018-09-12T08:22:53.541336500Z Found redis at 172.20.0.2
worker_1 | 2018-09-12T08:22:53.541400100Z Connecting to redis
worker_1 | 2018-09-12T08:33:54.478754500Z Connected to db
worker_1 | 2018-09-12T08:33:54.495682400Z Found redis at 172.20.0.2
worker_1 | 2018-09-12T08:33:54.496062600Z Connecting to redis
worker_1 | 2018-09-12T08:34:15.528315300Z Processing vote for 'b' by '2d4e42c6c94f4e53'
worker_1 | 2018-09-12T08:37:11.883353600Z Processing vote for 'a' by ‘2d4e42c6c94f4e53'

Starting a Container in Interactive Mode
Want a shell to debug startup commands without the container exiting on failure?
version: "3"
services:
web:
image: ubuntu:18.04
tty: true
stdin_open: true
entrypoint: "/bin/bash"
docker run -it ubuntu:18:04 /bin/bash
# volume mount if you need to with `-v
source:target`
with docker-compose run web with Docker only

‣ docker top will give you a list of all running processes in a container
‣ docker inspect (name | id) will give you ALL of the details about a given resource
Helpful Docker Commands
‣ You can use the --format flag and pass in a Go template
‣ For example, to get the IP(s) of a running container:
docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}'
$CONTAINER_ID

Running a Debugger
version: "3"
services:
result:
build: ./result
command: nodemon --inspect=0.0.0.0:5858 server.js
volumes:
- ./result:/app
ports:
- “5001:80"
- "5858:5858"
networks:
- front-tier
- back-tier
Maintain access to debugging tools by
publishing the ports.
You may also have to update the
command or entrypoint to access
debugging tools.

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DCEU 18: Developing with Docker Containers

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