Continuous Integration (CI) and Continuous Delivery (CD) are fundamental to DevOps and agile methodologies. They ensure that software is developed, tested, and delivered quickly and efficiently. CI and CD are more than just trending buzzwords. They are crucial processes that help teams deliver quality software at a high velocity. Understanding CI and CD is essential for anyone involved in software development or operations.

In this two-part series, we will demystify continuous integration vs. continuous delivery. In this part 1 article, we will discuss the basic concepts involved in Continuous Integration and Continuous Delivery. The article will highlight primary objectives of CI/CD, their benefits, CI/CD tools examples, key differences between CI and CD and real-world examples of CI/CD.

In part 2, we will discuss more advanced topics such as CI/CD practices, pipelines, security and general best practices for CI/CD implementation.

So, let’s get started with our part 1.

What is Continuous Integration (CI)?

Continuous Integration (CI) is a software development practice where developers frequently integrate their code changes into a shared repository, often multiple times a day. Each integration is verified by an automated build and automated tests to detect integration issues as early as possible.

The Primary Objectives of CI

• Integrating Code Frequently: Developers commit their code changes regularly, which helps to avoid integration issues that can occur when code changes accumulate over time. Frequent integration ensures that the main branch always contains a reliable version of the project.
• Automated Testing: Automated tests are run as part of the CI process to ensure that the new code does not break existing functionality. Tests can include unit tests, integration tests, and acceptance tests. The following is an example of a simple unit test using JUnit in Java.

Early Detection of Integration Issues: By integrating frequently and running automated tests, teams can detect and fix integration issues early in the development process. This approach helps to identify conflicts and errors quickly, reducing the cost and time to fix them.

Key Benefits of CI

• Reduced Integration Problems: Regular integration helps to identify and resolve conflicts early. This reduces the risk of integration problems. It also minimizes the time spent on merging changes and fixing integration issues.
• Improved Code Quality: Automated testing ensures that new code meets quality standards and does not introduce bugs. Code reviews and static analysis tools can be integrated into the CI pipeline to enforce coding standards and best practices.
• Faster Development Cycles: Frequent integrations and automated tests allow teams to identify and address issues quickly, accelerating the development process. This leads to shorter development cycles and faster delivery of features and bug fixes.

What Does a CI Tool Do?

Continuous Integration (CI) tools automate the process of building, testing, and integrating code changes into a shared repository. These tools ensure that each new code change is verified by an automated build and tested for quality. The goal is to catch integration issues early, maintain a deployable codebase, and ensure rapid feedback for developers.

Below is an overview of what a CI tool typically does:

• Code Integration – Developers commit code changes to a shared repository. The CI tool monitors this repository for any new changes.
• Automated Build – Once code changes are detected, the CI tool automatically triggers the build process. This involves compiling the code and preparing it for testing.
• Automated Testing – After the build, the CI tool runs automated tests, including unit tests, integration tests, and sometimes even end-to-end tests. This ensures the new code does not introduce bugs or break existing functionality.
• Feedback & Reporting – The CI tool provides immediate feedback to developers, highlighting any build failures, test failures, or integration issues. This feedback loop helps developers fix problems quickly and maintain a high-quality codebase.
• Continuous Integration Cycle – This process repeats continuously as developers commit new code, allowing for quick iterations and consistent code quality.

Diagram 1: Continuous Integration Workflow

Overview of CI Tools

Continuous Integration (CI) tools are essential for automating the process of integrating code changes, building the application, and running tests. While many CI tools share common features like automated builds and testing, each has its strengths, popularity, and ideal use cases.

Some tools are more popular due to their extensive plugin ecosystems, while others are favoured for their seamless integration with specific platforms like GitHub or Docker. Below, we explore some of the most popular CI tools and what sets them apart.

Example Tools for CI

Now that we understand what CI tools do, let’s look at some popular CI tools and how they implement the CI process.

Jenkins

Jenkins is an open-source automation server that is highly popular due to its flexibility and vast plugin ecosystem. It can support building, deploying, and automating nearly any project, making it a go-to solution for many teams.

• Popularity: Jenkins is widely used in the industry because it is open-source and has over 1,800 plugins that extend its capabilities.
• Strengths: Flexibility, extensive plugin support, and a strong community.

Jenkins uses a file called Jenkinsfile to define these stages. The following code snippet shows an example of the Jenkins Pipeline syntax:

Explanation

The pipeline begins by defining the agent any, which tells Jenkins to run the pipeline on any available agent.

The pipeline has two stages: Build and Test.

• In the Build stage, the sh 'mvn clean package' command is executed, which uses Maven to clean and package the Java project into a distributable format (e.g., a JAR file).
• In the Test stage, the sh 'mvn test' command runs the project’s tests using Maven, ensuring that the code is working as expected before it progresses further in the pipeline.

These stages are executed in sequence, ensuring that the code is built before testing begins.

Travis CI

Travis CI is particularly popular among open-source projects. It integrates seamlessly with GitHub, automatically triggering builds and tests for each new pull request. Its ease of use and tight integration with GitHub make it a favorite for open-source maintainers.

• Popularity: Travis CI is well-known in the open-source community and has been widely adopted by projects hosted on GitHub.
• Strengths: Simple setup, strong GitHub integration, and free for open-source projects.

1. It uses a .travis.yml configuration file to define the CI process.The following code snippet shows an example of the Travis CI Pipeline syntax:

Explanation

Travis CI first specifies that the pipeline is for a java project. The script section contains the steps Travis CI will execute in order:

• First, mvn clean package will build and package the Java project.
• Then, mvn test will execute the tests to verify that the code behaves as expected.

These commands are executed automatically every time new code is pushed to the repository, ensuring the codebase remains functional.

CircleCI

CircleCI is favored for its speed and efficiency. It supports rapid building, testing, and deployment, making it ideal for teams that require fast feedback and continuous delivery. CircleCI also offers powerful features like parallelism and Docker support, which allow for more complex build processes.

• Popularity: CircleCI is popular among teams that prioritize speed and efficiency, particularly those leveraging Docker.
• Strengths: Speed, parallelism, Docker integration, and scalability.

1. It uses a config.yml file located in the .circleci directory of your project to define the build and test process. The following code snippet shows an example of the CircleCI Pipeline syntax:

Explanation

The pipeline specifies version: 2.1, which defines the configuration version.

The build job is defined using a Docker image (circleci/openjdk:11) to provide the Java runtime environment.

Steps

• checkout retrieves the latest code from the repository.
• run: mvn clean package compiles and packages the code into a distributable format.
• run: mvn test executes the tests to ensure the code is working properly.

CircleCI allows this pipeline to be executed in an isolated Docker environment, ensuring consistency across builds and reducing dependencies on local machine configurations.

What is Continuous Delivery (CD)?

Continuous Delivery (CD) is a software development practice where code changes are automatically prepared for a production release.. It ensures that the software can be reliably released at any time and that deploying new releases can be done quickly and sustainably. CD extends Continuous Integration (CI) by automating the release process all the way to production, minimizing the risks and manual interventions required in deploying new code.

How Does Continuous Delivery Work?

The CD process involves several key stages:

1. Build: After developers commit their code, the system automatically compiles and builds the application, ensuring it is ready for testing and deployment.
2. Automated Testing: The built code is subjected to a series of automated tests. These tests ensure that the code is functional and does not introduce new bugs or regressions.
3. Staging: The code is deployed to a staging environment that closely mimics the production environment. This stage allows for further testing, such as user acceptance testing (UAT), in an environment that is almost identical to production.
4. Deployment Approval: In some cases, deployments to production may require manual approval. This step acts as a safety check before the code is released to users.
5. Production Deployment: Once approved, the code is automatically deployed to the production environment. This step is streamlined to ensure minimal downtime and disruption to users.

Below is a diagram that illustrates the Continuous Delivery process:

The Primary Objectives of CD

• Ensuring the Code is Always in a Deployable State: The codebase is always in a state that could be released into production. This involves rigorous automated testing and quality checks.
• Automating the Release Process: The release process is automated to minimize manual intervention and reduce the potential for human error. This includes steps like environment provisioning, database migrations, and deployment.

The following is an example of an automated deployment script using Ansible:

• Reducing Manual Intervention: It automates repetitive tasks; therefore, teams can focus on more complex tasks that require human intervention. This reduces errors and speeds up the deployment process.

Key Benefits of CD

• Faster and Reliable Deployments: Automated release processes enable faster and more reliable deployments. This reduces the time from code commit to production deployment.
• Reduced Deployment Risks: Automated testing and deployment reduce the risk of issues arising during deployment. Rollback mechanisms and canary deployments can also be used to mitigate risks.
• Improved Feedback Loops: Continuous feedback from automated testing and monitoring helps teams to quickly identify and resolve issues. This leads to faster iterations and improvements.

Example Tools for CD

When choosing a Continuous Delivery (CD) tool, several factors should be considered, including compatibility with your existing CI pipeline, ease of integration with cloud providers, support for automated testing, scalability, and community support. Below, we explore some of the popular CD tools, highlighting their key features and differences.

Spinnaker

Spinnaker is an open-source, multi-cloud continuous delivery platform. It is particularly strong in environments that require multi-cloud deployments, providing a robust framework for deploying and managing applications across various cloud providers such as AWS, Google Cloud, and Microsoft Azure.

Why Choose Spinnaker?

Spinnaker is ideal for teams that need to manage complex, multi-cloud deployments. Its strong integration with cloud providers and advanced deployment strategies like blue/green and canary deployments make it a powerful tool in environments where high availability and resilience are critical.

The following code snippet shows an example of a Spinnaker pipeline configuration:

Explanation

• Pipeline Configuration: This JSON file defines a Spinnaker pipeline for an application named example-app hosted on GitHub.
• Bake AMI: The bake stage is responsible for creating an Amazon Machine Image (AMI) that can be deployed. This image typically contains the application code, configurations, and necessary dependencies.
• Deploy to Prod: The deploy stage deploys the baked AMI to the production environment.

This pipeline, when executed, would first create a deployable image and then proceed to deploy it to the production environment, ensuring consistency and reliability in the deployment process.

Jenkins

Jenkins, widely known for its CI capabilities, can also be configured for continuous delivery. It integrates with various deployment tools and cloud services to automate the deployment process, making it a versatile choice for teams already using Jenkins for CI.

Why Choose Jenkins?

Jenkins is a great choice for teams that already use it for CI. Its extensive plugin ecosystem allows it to be easily extended to handle CD tasks, and its strong community support ensures that you can find solutions to almost any problem you might encounter. The following code snippet shows an example of a Jenkins deployment stage:

Explanation

• Build Stage: This stage compiles the application using Maven (mvn clean package), creating a deployable artifact (e.g., myapp.war).
• Test Stage: The test stage runs the application’s test suite to ensure the build is stable (mvn test).
• Deploy Stage: The deployment stage securely copies (scp) the artifact to the deployment server and places it in the specified path.

Upon execution, Jenkins would automate the entire process, from building and testing the application to deploying it to the specified server.

Bamboo

Bamboo is a CI and CD tool that integrates seamlessly with other Atlassian products like Jira and Bitbucket. It supports automated builds, tests, and deployments, making it a comprehensive CI/CD solution.

Why Choose Bamboo?

Bamboo is ideal for teams using the Atlassian suite of tools. Its seamless integration with Jira and Bitbucket makes it easier to manage the entire software delivery pipeline from a single interface, improving visibility and traceability across the development lifecycle.

The code snippet below shows an example of a Bamboo deployment project configuration:

Explanation

• Build Stage: This stage would typically compile and package the application. However, in this snippet, the build stage is assumed to have been completed earlier, perhaps in a different pipeline or manually before the deployment stage. Therefore, this configuration focuses on the deployment rather than repeating the build process.
• Test Stage: Similar to the build stage, testing is not explicitly detailed in this snippet. It is assumed that testing has already been conducted, either as part of an earlier pipeline or manually. The focus here is on deploying a pre-tested artifact.
• Deploy Stage: The deploy stage handles the deployment of the application.
  • scp target/myapp.war user@server:/path/to/deploy: This command copies the packaged application (myapp.war) to the specified directory on the deployment server.
  • ssh user@server 'systemctl restart myapp: After copying the artifact, this command restarts the application service on the server to apply the new deployment.

The Bamboo snippet is streamlined for deployment purposes, under the assumption that the build and test processes are handled elsewhere. This allows for a focused deployment stage that moves a tested artifact to production and restarts the application to ensure the new version is live.

Key Differences Between CI and CD:

While both CI and CD aim to improve the software development process, they focus on different stages and aspects of the pipeline.

Main focus for CI and CD

Continuous Integration is primarily concerned with integrating code changes. It ensures they do not break the build or existing functionality through automated testing. CI involves frequent code commits, automated builds, and testing to ensure code quality and integration stability.

On the other hand, Continuous Delivery extends CI by automating the deployment process. It ensures that the code is always in a deployable state and can be released to production at any time. Furthermore, CD involves additional steps like environment provisioning, automated deployments, and post-deployment testing.

CI Pipeline stages are code commit, build, and automated tests. Whereas, CD Pipeline Stages include code commit, build, automated tests, and deployment.

Cultural and Procedural Shifts

CI Implementation requires a cultural shift towards frequent code commits and a robust automated testing culture. Developers need to embrace automated testing and integrate their changes frequently.

On the other hand, CD implementation involves further cultural shifts towards automating the release process and maintaining a deployable codebase at all times. Teams need to automate their deployment processes and ensure that the code is always in a releasable state.

Bringing CI and CD Together

Continuous Integration (CI) and Continuous Delivery (CD) are often seen as two separate stages in the software development lifecycle, but in reality, they are closely intertwined and work in tandem to achieve the broader goals of DevOps and Agile methodologies. While CI focuses on ensuring that code changes are integrated frequently and that these integrations are reliable through automated testing, CD builds upon that foundation by automating the deployment process to ensure that the software is always in a releasable state.

Together, CI and CD form a unified pipeline that accelerates the journey from code commit to production deployment. CI ensures that the code is consistently stable and of high quality, reducing integration issues and improving collaboration across teams. CD takes that stable code and streamlines the process of releasing it, minimizing the need for manual intervention and reducing the risks associated with deployments. This combination allows teams to deliver features, updates, and bug fixes faster and more reliably, helping organizations meet customer demands and market conditions efficiently.

Wrapping Up

By embracing both CI and CD, teams can achieve a continuous flow of software delivery, where every code commit is tested, integrated, and ready for production deployment. This results in shorter development cycles, increased developer productivity, and a higher level of confidence in the quality of the software being delivered.

In the next part of this series, we will explore more advanced topics, including the CI/CD pipeline in detail, best practices for implementation, and how security can be integrated into the CI/CD process. Stay tuned for Part 2, where we will dive deeper into these concepts.