SPRING BOOT

DOCKER
BASICS

ROHAN THAPA
THAPAROHAN2019@GMAIL.COM
 What is a Docker?
Docker is a platform for developing, shipping,
and running applications inside containers.

Containers are isolated environments that

encapsulate everything an application needs
to run, including the code, runtime, libraries,
and system tools, ensuring that the
application runs consistently across different
computing environments.

Containerization isolates applications,

avoiding conflicts between libraries and
dependencies.
Portability is one of Docker's primary
advantages, meaning you can "build once,
run anywhere."
 Why Docker?
Consistency Across Environments:
Applications in Docker containers will run
the same regardless of the environment
(development, testing, production).
Efficiency: Containers use fewer resources
than virtual machines because they don’t
bundle a full operating system.
Fast Deployment: Containers can be
quickly created, deployed, and scaled,
facilitating continuous integration and
delivery (CI/CD).
Isolation: Each Docker container runs in
isolation from others, avoiding
dependency conflicts.
Scalability: Containers can be easily scaled
across clusters of machines.
 Key Docker Concepts
Docker Containers

Containers are lightweight, stand-alone,

executable packages of software that
include everything needed to run a piece
of software: code, runtime, system tools,
libraries, and settings.
Difference from VMs: Containers share the
same OS kernel, unlike VMs, which
virtualize entire hardware, making
containers faster and more lightweight.
 Key Docker Concepts
Docker Images

Images are the blueprints of containers.

They include the application and its
dependencies but are immutable and read-
only. Containers are instances of images.
Layers: Images are built in layers, with each
command in a Dockerfile creating a new
layer. This layering allows for efficient
storage and reuse of common layers.
 Key Docker Concepts
Dockerfile

A Dockerfile is a script containing a set of

instructions that Docker uses to create a
container image. Each instruction in a
Dockerfile creates a new layer in the
image.
Common Dockerfile Instruction
1. FROM :
Specifies the base image for the Docker image.

2.LABEL
Adds metadata to an image in the form of key-value
pairs.

3.WORKDIR
Sets the working directory inside the container for
subsequent commands.

4.COPY
Copies files or directories from the host filesystem to
the container.
Common Dockerfile Instruction
5.ADD
Similar to COPY, but also supports extracting tar files
and downloading URLs.

6.RUN
Executes commands inside the container during the
build process.

7.CMD
Specifies the default command to run when a
container starts (overridden by docker run
command).

8.ENTRYPOINT
Configures the container to run as an executable
with a command that can't be overridden.
Common Dockerfile Instruction
9.ENV
Sets environment variables inside the container.

10.ARG
Defines build-time variables (accessible only during
the build process).

11.EXPOSE
Informs Docker that the container listens on specific
network ports.

12.VOLUME
Defines a mount point with a specific path in the
container to persist data.
 Key Docker Concepts
Docker Hub

Docker Hub is a cloud-based repository

where Docker users can push and pull
container images. It’s the default registry
used by Docker, offering both official
images and user-contributed images.

Docker Volumes

Volumes are used to persist data

generated by a container. Volumes are
stored outside the container filesystem, so
they aren't tied to the lifecycle of a
container.
 Key Docker Concepts
Docker Networks

Docker allows containers to communicate

with each other using different networking
modes, including:
Bridge: Default, allows containers to
communicate on the same host.
Host: Shares the host’s network stack.
Overlay: Enables swarm services to
communicate across multiple Docker
daemons.
 Docker Architecture
Docker has a client-server architecture:

Docker Client: The primary user interface

for Docker. Users interact with Docker by
issuing commands using the Docker CLI.
Docker Daemon: Responsible for building,
running, and managing containers.
Docker Registry: A place where Docker
images are stored. Docker Hub is a public
registry.
Docker Objects: Images, containers,
networks, and volumes are the objects
Docker uses.
 Core Docker Operations
Basic Docker Commands

docker pull: Fetches an image from a

registry.
docker build: Builds an image from a
Dockerfile.
docker run: Runs a container from an
image.
docker ps: Lists running containers.
docker stop: Stops a running container.
docker rm: Removes a stopped container.
docker exec: Runs a command inside a
running container
 Basic Docker Commands
check version

pull image from dockerhub

list images
 Basic Docker Commands
search images

run the image

 Basic Docker Commands
view container and stop container

remove the container

 Basic Docker Commands
remove the image
 Basic Docker Commands
docker login :
Logs into a Docker registry (usually Docker
Hub). You will be prompted to enter your
credentials.

docker logout : Logs out from a Docker

registry.
 Core Docker Operations
Managing Containers
docker logs: Retrieves logs from a
container.
docker stats: Shows resource usage
statistics for containers.

Docker Compose
Docker Compose is used to define and
manage multi-container applications. You
create a docker-compose.yml file, which
defines services, networks, and volumes.
 Advanced Docker Concepts
Docker Swarm
Docker Swarm is Docker's native
clustering and orchestration tool. It allows
Docker hosts to group together into a
cluster, where containers can be scaled
and managed across multiple machines.

Kubernetes
Kubernetes is an open-source container
orchestration platform, which is often
used with Docker to automate the
deployment, scaling, and management of
containerized applications across clusters
of machines.
 Advanced Docker Concepts
Docker in CI/CD

Docker plays a crucial role in Continuous

Integration and Continuous Delivery
pipelines. It allows teams to run automated
tests, build images, and deploy the same
container to any environment (dev,
staging, production), ensuring consistency.
 Docker Security
Docker offers several layers of security:

Namespaces: Provide isolation for a

container’s processes, users, file system,
and network.

Control Groups (Cgroups): Limit resources

a container can consume (CPU, memory,
etc.).

Seccomp Profiles: Limit system calls that

containers are allowed to make, reducing
potential attack vectors.
 Example:
Here’s a basic example of how to containerize
a Spring Boot application and run it with
Docker:

1. Create a Spring Boot Application

 Example:
2. Create a Dockerfile
Next, we need to create a Dockerfile. This file
contains the instructions Docker uses to
create the container.

In the root directory of your Spring Boot

application (where pom.xml or build.gradle is
located), create a file called Dockerfile:
 Example:
Explanation:
Firstly we add a finalName tag in pom.xml
to set the fix name for .jar file.

Then we compile the Spring Boot

application and create a .jar file.

Then we use a lightweight OpenJDK image

to run the .jar file. The resulting container
will run on Java 22, and expose port 9898
 Example:
3. Build the Docker Image
After creating the Dockerfile, you can now
build the Docker image.
Open a terminal in the root directory of your
Spring Boot application and run the following
command:

This command builds the Docker image from

the Dockerfile and tags it as springbootimage.
 Example:
4. Run the Docker Container
Now that we have the Docker image, we can
run it in a container. Run the following
command:

-p 9898:8080: This maps the container’s port

8080 to your local machine's port 9898.
 Example:
5. Test the Application
Once the container is running, open your
browser and go to http://localhost:9898/api.
You should see the message:
Docker vs Virtual Machines
Benefits of Dockerizing a Spring Boot
Application
Consistency: The application will behave
the same in any environment because it
includes all dependencies.
Scalability: Docker containers can be
easily replicated and deployed across
multiple hosts.
Portability: You can ship the application as
a single image that can run anywhere
Docker is installed.
Isolation: Each Docker container runs in its
own environment without affecting the
host system or other containers.
 Conclusion
Docker has transformed the way we develop,
test, and deploy software. It provides a
lightweight, scalable solution for
containerizing applications, ensuring
consistency across environments.

Whether you’re using Docker for local

development, CI/CD, or managing production
workloads, Docker’s flexibility and speed make
it an indispensable tool for modern software
development.

With Docker, the phrase "It works on my

machine!" becomes irrelevant — it works
everywhere.
Thank You
Rohan Thapa
thaparohan2019@gmail.com