What is Continuous Deployment?
Continuous Deployment (CD) is a software engineering practice that automatically releases code updates to production. CD uses automated testing to ensure that code changes are correct and stable before deployment. It typically follows these stages:
- Code is written and changed
- The code is automatically built and tested
- If the code passes the tests, it is deployed to production
- Users receive the updates and provide feedback
Timothy Fitz was probably the first to define Continuous Deployment as a practice:
This is a software release process implementation of the classic Fail Fast pattern. The closer a failure is to the point where it was introduced, the more data you have to correct for that failure. … In a software release process Fail Fast means releasing undeployed code as fast as possible, instead of waiting for a weekly release to break.
Benefits of Continuous Deployment include:
- Faster releases: CD can save time and money by allowing for quicker releases
- Better quality: CD can reduce the time spent deploying and testing, which allows for more time to improve release quality
- Flexibility: CD allows developers to quickly fix bugs and issues based on customer feedback
- Collaboration: CD makes it easier for development and operations teams to work together
Here are a few best practices for effective Continuous Deployment:
- Use strong automated testing and monitoring processes
- Have a culture that embraces automation, collaboration, and trust
- Be realistic about what is required
- Use progressive delivery techniques to limit the risk to the user base
- Maintain a strong Continuous Integration foundation
- Build a strong testing strategy
- Invest in a continuous monitoring practice
- Shift left and emphasize security across the SDLC
This is part of an extensive series of guides about DevOps.
How does a Continuous Deployment pipeline work?
A Continuous Deployment pipeline automates the process of deploying code changes to production. The pipeline typically consists of several stages, each designed to validate and verify the new code before it reaches end-users.
Here’s a breakdown of how a Continuous Deployment pipeline works:
- Code commit: Developers commit their code changes to a version control system (VCS) like Git. Each commit triggers the Continuous Deployment pipeline to start.
- Build: The pipeline begins by compiling the code and creating build artifacts. This step ensures that the codebase is in a state that can be deployed.
- Automated testing: After the build, the pipeline runs a suite of automated tests. These tests usually include:
- Unit tests: Verify individual components or functions.
- Integration tests: Check that different modules work together correctly.
- End-to-end tests: Simulate user interactions to ensure the application works as expected.
- Performance/load tests: Assess how the application performs under various conditions.
- Dynamic code analysis: Automated tools can be used to run the application and analyze the code for potential bugs, security vulnerabilities, and code quality issues.
- Deployment to staging: Once the code passes all tests and analysis, it is deployed to a staging environment. This environment closely mimics the production environment and allows for further testing.
- Deployment to production: After passing all checks, the code is automatically deployed to the production environment. Deployment strategies such as blue/green deployments or canary releases can be used to minimize risks and eliminate downtime.
- Continuous monitoring: Post-deployment, continuous monitoring tools track the application’s performance and health. Metrics like response time, error rates, and resource usage are monitored to ensure the deployment is successful.
- User feedback: End users report on issues with the updates and highlight areas they approve. This informs the next update and allows teams to improve the code continuously.
Continuous Deployment versus Continuous Integration
Continuous integration (CI): CI focuses on integrating code changes from multiple developers into a shared repository multiple times a day. The primary goal is to detect integration issues early, allowing developers to address them promptly while they are still small. CI involves the following steps:
- Code commit: Developers frequently commit code to a central repository.
- Automated build: Each commit triggers an automated build to compile the code.
- Automated testing: A suite of automated tests runs to verify the functionality of the code changes.
- Feedback: Developers receive immediate feedback on the build and test results, enabling quick fixes for any issues.
CI aims to maintain a consistent and stable codebase, ensuring that new code changes do not break the existing functionality. It emphasizes the early detection of defects, improving code quality and collaboration among team members.
Continuous Deployment: Extends the principles of CI by automating the entire release process, from code commit to production deployment. In addition to the CI steps, Continuous Deployment includes:
- Automated deployment: Successful builds and tests trigger automatic deployment to production without manual intervention.
- Continuous monitoring: Post-deployment monitoring ensures the application performs as expected in the live environment.
While CI ensures code changes are regularly integrated and tested, Continuous Deployment ensures that these changes are automatically deployed to production, providing users with immediate access to new features and improvements.
Continuous Deployment versus Continuous Delivery
Continuous Deployment and Continuous Delivery share many similarities but differ in the extent of automation in the release process.
Continuous Delivery: Involves automating the software release process up to the production environment but includes a manual step before deployment. The key steps in Continuous Delivery are:
- Automated testing: Like CI and Continuous Deployment, Continuous Delivery involves rigorous automated testing to ensure code quality.
- Staging deployment: Code changes are deployed to a staging environment for further validation.
- Manual approval: Before deploying to production, a manual approval step, such as a code review or stakeholder sign-off, is required.
Continuous Delivery aims to make releases predictable and less risky. While the code is always ready for production, the manual approval step provides an additional layer of verification, allowing for thorough checks and validation before final deployment.
Continuous Deployment: Automates the entire process, including the final deployment to production. The absence of a manual approval step distinguishes Continuous Deployment from Continuous Delivery. This approach is suited for organizations with robust testing and monitoring frameworks that can confidently rely on automated processes to ensure code quality.
In summary:
- Continuous Delivery: Automates up to staging environment, manual approval required before deployment to production.
- Continuous Deployment: Fully automates the release process, including deployment to production.
While both practices aim to enhance the speed and reliability of software delivery, the choice between them depends on the organization’s risk tolerance and the maturity of its automated testing and monitoring processes.
Related content: Read our guide to Continuous Deployment software