DCSF19 Containers for Beginners

Michael Irwin - @mikesir87
Virginia Tech; Docker Captain
Containers
for Beginners

@mikesir87
Disclaimer: I cannot explain
sprankle pods either!

@mikesir87
Quick History of Shipping
Source: https://www.publicdomainpictures.net/en/view-image.php?image=275355 Source: https://en.wikipedia.org/wiki/Rail_freight_in_Great_Britain Source: https://pxhere.com/en/photo/553345

@mikesir87
Shipping in Software
Source: https://www.usafe.af.mil/News/Photos/igphoto/2000887438/

@mikesir87
Either of these two scenarios
sound familiar to you?

@mikesir87
Welcome!
Glad to have
you on the
team!
Clone the repo,use the wiki forsetup instructions,and update the
docs as needed.Good luck!

@mikesir87
Creating Images
• Best practice is to use a Dockerfile
• A text ﬁle that serves as a script to build an image
• Build using the docker build command
FROM node
WORKDIR /app
COPY package.json yarn.lock .
RUN yarn install
COPY src ./src
CMD ["node", "src/index.js"]

@mikesir87
Sharing Images
• Once built, the image is only available locally
• To share, push it to a registry using docker push
• Docker Hub is the default registry
• Docker EE includes the Docker Trusted Registry
• Many other third-party oﬀerings available too
• Once shared, others can pull the image
Source: https://landscape.cncf.io

@mikesir87
Let’s build an image!

@mikesir87
What’s a container then?
• While a container looks like a VM, it isn’t!
• A container is just another process on the machine
• It uses namespaces and control groups (cgroups) to provide
isolation
• Namespaces include network, process, user, IPC, mount, and others
• To run a container, use the docker container run command

@mikesir87
Containers vs VMs
Infrastructure
Host Operating System
Hypervisor
Guest OS
Bins/Libs
App 1
Guest OS
Bins/Libs
App 2
Guest OS
Bins/Libs
App 3
Infrastructure
Operating System
Bins/Libs
App 1
Bins/Libs
App 2
Bins/Libs
App 3
Docker
Daemon

@mikesir87
Image Layering
• Images are composed of layers of filesystem changes
• Each layer can add or remove from the previous layer
• Each layer’s filesystem changes are stored as a single tar file
• Each command in a Dockerfile creates a new layer
• Use the docker image history command to see the layers and the
command that was used to create each layer

@mikesir87
Layer contents
file1 file2 file3 file4
file2 file5
file1 file2 file3 file4 file5
Layer 1
Layer 2
Merged
• Layers are unioned together to make a full filesystem
• Each layer can add files as needed
• Files in “higher” layers replace the same file in “lower” layers
• The container uses the “merged” view

@mikesir87
What about deleted files?
● Deleted files are represented in a layer as a “whiteout” file
● Whiteout files are only used by the filesystem driver and not visible
in the merged filesystem
file2 file5
Layer 1
Layer 2
Merged
.wh.file4 Layer 3

@mikesir87
WARNING!
Be careful what you put into images.
Deleted files might not actually be
gone!

@mikesir87
Two Best Practices Incoming!

@mikesir87
Clean up as you go!
● Don’t wait until the end of the Dockerﬁle to “clean” up
● Chain RUN commands together to clean things as you go
FROM ubuntu
RUN apt-get update
RUN apt-get install -y python python-pip
RUN pip install awscli
RUN apt-get autoremove --purge -y python-pip
FROM ubuntu
RUN apt-get update &&
apt-get install -y python python-pip &&
pip install awscli &&
apt-get autoremove --purge -y python-pip &&
rm -rf /var/lib/apt/lists/*
Net change of image size from
512MB to 183MB (64% reduction)

@mikesir87
Keep images tight and focused
• Only install the deps/tools/packages that are necessary
• Use multi-stage builds to separate build-time and run-time
dependencies
FROM node AS build
WORKDIR /usr/src/app
COPY package.json yarn.lock .
RUN yarn install
COPY public ./public
COPY src ./src
RUN yarn build
FROM nginx:alpine
COPY nginx.conf /etc/nginx/nginx.conf
COPY --from=build /usr/src/app/build /usr/share/nginx/html
Sample multi-stage build for a React app

@mikesir87
How do you persist data?

@mikesir87
● Volumes provide the ability to persist/supply data
● Bind mount volumes
○ You choose where to persist the data
○ Example: -v $HOME/mysql-data:/var/lib/mysql
● Named volumes
○ Let Docker choose where to persist the data
○ Can use docker volume inspect to ﬁnd actual location
○ Example: -v mysql-data:/var/lib/mysql
Volumes

@mikesir87
Show me these volumes!

@mikesir87
Docker Compose
• Makes defining and running multi-container apps super easy
• Uses a YAML file for configuration (docker-compose.yml)
• Often included in project source repo at the root of the project
• With a single command, start all containers/services for an app
• Tool is bundled with Docker Desktop

@mikesir87
Docker Networking
• Think of networking in terms of communication boundaries/isolation
• If two containers are on the same network, they can talk to each other
• Docker runs its own DNS resolver on each network
• Allows it to resolve IP addresses of other containers using “aliases”
API1
Database
Reverse Proxy
React App
API2
Cache

@mikesir87
Quick compose demo!

@mikesir87
Container Orchestration
• Orchestration provides the ability to manage the running of
container workloads, often over a fleet of machines
• You define the expected state (the desired state)
• The system then tries to make actual state reflect expected state

@mikesir87
Actors in Orchestration
• Every orchestrator has the concept of two types
of nodes
• Managers
• Serve as the brains of the cluster
• Maintain state and schedule work
• Sometimes called masters
• Worker nodes
• Perform the actual work, as instructed by a manager
• Sometimes called agents or nodes

@mikesir87
Various Orchestrators
• Docker Swarm
• Shipped with the Docker engine
• Very user friendly and easy to get up and running
• Satisﬁes most needs, though not all; built to be extensible, but takes some work
• Kubernetes
• Spun out of work done within Google and contributed to CNCF
• Think of it more as a toolkit - so not as easy to get up and running
• Very conﬁgurable and extensible
• Amazon ECS
• Made by Amazon Web Services and provided for free
• Provides deep integration with AWS resources (IAM, ALBs, Auto-scaling, etc.)

@mikesir87
• Containers/images are here to standardize application packaging
• No longer require host conﬁguration
• Docker Compose builds on the abstraction to make multi-service apps easier
• Container orchestration builds on this idea
• Be mindful of how you build your images and what you include
• Volumes allow data to be persisted longer than the container
• Networking serves provides communication paths/isolation
Recap

@mikesir87
WARNING!
Containers are NOT a silver bullet
that will fix your company culture

Thank you!
Rate the session!
Keep in touch!
@mikesir87; mikesir87@vt.edu

DCSF19 Containers for Beginners

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DCSF19 Containers for Beginners