Continuous delivery is the ability to release changes of all kinds on demand quickly, safely, and sustainably. Teams that practice continuous delivery well are able to release software and make changes to production in a low-risk way at any time—including during normal business hours—without impacting users.
You can apply the principles and practices of continuous delivery to any software context, including the following:
- Updating services in a complex distributed system.
- Upgrading mainframe software.
- Making infrastructure configuration changes.
- Making database schema changes.
- Updating firmware automatically.
- Releasing new versions of a mobile app.
When your team practices continuous delivery, you can answer "yes" to the following questions:
- Is our software in a deployable state throughout its lifecycle?
- Do we prioritize keeping the software deployable over working on new features?
- Is fast feedback on the quality and deployability of the system we are working on available to everyone on the team?
- When we get feedback that the system is not deployable (such as failing builds or tests), do we make fixing these issues our highest priority?
- Can we deploy our system to production, or to end users, at any time, on demand?
Continuous delivery is commonly conflated with continuous deployment, but they are separate practices. Continuous deployment is when teams try to deploy every code change to production as soon as possible. Continuous deployment works well for web services, but can't be applied to software such as firmware or mobile apps. Continuous delivery is applied to all kinds of software including firmware and mainframe systems, and in highly regulated environments. You can and should start with continuous delivery, even if you never intend to start using continuous deployment.
Continuous delivery and continuous deployment are mistakenly viewed as risky and not suited to regulated or safety critical domains. In fact, the goal of continuous delivery is to reduce software risk, and DORA research has shown consistently that high performers achieve higher levels of reliability and availability. The technical practices that drive continuous delivery—continuous testing, shifting left on security, and comprehensive testing and observability—are even more important in highly regulated and safety-critical domains. Continuous delivery has been successfully applied many times in highly regulated domains such as financial services and government.
Although continuous delivery is possible for all kinds of software, it is hard work. Nevertheless it provides significant benefits. DevOps Research and Assessment (DORA) research shows that doing well at continuous delivery provides the following benefits:
- Improves software delivery performance, measured in terms of the four key metrics, as well as higher levels of availability.
- Leads to higher levels of quality, measured by the percentage of time teams spend on rework or unplanned work (as shown in the 2016 State of DevOps Report pp25-26, and the 2018 State of DevOps Report pp27-29).
- Predicts lower levels of burnout (physical, mental, or emotional exhaustion caused by overwork or stress), higher levels of job satisfaction, and better organizational culture.
- Reduces deployment pain, a measure of the extent to which deployments are disruptive rather than easy and pain-free, as well as the fear and anxiety that engineers and technical staff feel when they push code into production.
- Impacts culture, leading to greater levels of psychological safety and a more mission-driven organizational culture.
The following diagram shows how a set of technical practices impacts continuous delivery, which in turn drives the outcomes listed above:
Continuous delivery is only one aspect of driving the previously discussed outcomes, albeit a critical one. Other cultural and organizational capabilities discussed in the DORA research program also help drive these outcomes. You can achieve continuous delivery by implementing the technical practices described in this document.
Implementing continuous delivery
DORA research found that the following technical capabilities drive the ability to achieve continuous delivery. Transformational leadership within the organization also drives the implementation of many of these technical capabilities.
To help your team get higher throughput and lower risk releases, implement the following continuous delivery practices:
- Test automation: The use of comprehensive automated test suites primarily created and maintained by developers. Effective test suites are reliable—that is, tests find real failures and only pass releasable code.
- Deployment automation: The degree to which deployments are fully automated and do not require manual intervention.
- Trunk-based development: Characterized by fewer than three active branches in a code repository; branches and forks having very short lifetimes (e.g., less than a day) before being merged into mainline; and application teams rarely or never having code lock periods when no one can check in code or do pull requests due to merging conflicts, code freezes, or stabilization phases.
- Shift left on security: Integrating security into the design and testing phases of the software development process. This process includes conducting security reviews of applications, including the information security team in the design and demonstration process for applications, using pre-approved security libraries and packages, and testing security features as a part of the automated test suite.
- A loosely coupled architecture: Architecture that lets teams test and deploy their applications on demand, without requiring orchestration with other services. Having a loosely coupled architecture allows your teams to work independently without relying on other teams for support and services, which in turn enables them to work quickly and deliver value to the organization.
- Empowering teams to choose tools: Teams that can choose which tools to use do better at continuous delivery. No one knows better than practitioners what they need to be effective.
- Continuous integration (CI): A development practice where code is regularly checked in, and each check-in triggers a set of quick tests to discover regressions, which developers fix immediately. The CI process creates canonical builds and packages that are ultimately deployed and released.
- Continuous testing: Testing throughout the software delivery lifecycle rather than as a separate phase after dev complete. With continuous testing, developers and testers work side by side. High performers practice test-driven development, get feedback from tests in less than ten minutes, and continuously review and improve their test suites (for example, to better find defects and keep complexity under control).
- Version control: The use of a version control system, such as Git or Subversion, for all production artifacts, including application code, application configurations, system configurations, and scripts for automating build and configuration of environments.
- Test data management: Effective practices include having adequate data to run your test suite, the ability to acquire necessary data on demand, and the data not limiting the number of tests you can run. We caution that your teams should minimize, whenever possible, the amount of test data needed to run automated tests.
- Comprehensive monitoring and observability: Allows teams to understand the health of their systems. Effective solutions enable teams to monitor predefined metrics, including system state as experienced by users, as well as allowing engineers to interactively debug systems and explore properties and patterns as they emerge.
- Proactive notifications: Monitoring system health so that teams can preemptively detect and mitigate problems.
- Database change management: Database changes don't slow teams down if they follow a few key practices, including storing database changes as scripts in version control (and managing these changes the same way as production application changes), making database changes visible to everyone in the software delivery lifecycle (including engineers), and communicating with all parties when changes to the application require database changes.
- Code maintainability: Systems and tools that make it easy for developers to change code maintained by others, to find examples in the codebase, to reuse other people's code, and to add, upgrade, and migrate to new versions of dependencies without breaking their code.
While continuous delivery is often combined with continuous integration and shortened to CI/CD, research shows that continuous integration is only one element of implementing continuous delivery. To achieve reliable, low-risk releases, you need close collaboration between everyone involved in the software delivery process, not just software developers, and your team needs to adopt new ways of working and learn new skills.
Common pitfalls of implementing continuous delivery
Some organizations mistakenly believe that they can implement continuous delivery by doing their existing deployment process more often. However, implementing the technical capabilities that drive continuous delivery typically requires significant process and architectural changes. Increasing the frequency of deployments without improving processes and architecture is likely to lead to higher failure rates and burned out teams.
Many descriptions of continuous delivery focus on the tooling and patterns, such as the deployment pipeline that takes changes from version control to production. However, using modern tooling without implementing the necessary technical practices and process change described in this document won't produce the expected benefits.
The following diagram shows the J curve that DORA research has found to be typical of transformation programs. To emerge from the bottom of the J curve, your team needs to include process redesign and simplification, architectural improvement, and capability and skills development, along with automation and tooling.
In the diagram, the following stages are labeled:
- At the beginning of the curve, teams begin transformation and identify quick wins.
- In an initial improvement, automation helps low performers progress to medium performers.
- In a decrease to efficiency—the bottom of the J curve—automation increases test requirements, which are dealt with manually. A large amount of technical debt blocks progress.
- As teams begin to come out of the curve, technical debt and increased complexity cause additional manual controls and layers of process around changes, slowing work.
- At the top of the curve, relentless improvement work leads to excellence and high performance. High and elite performers leverage expertise and learn from their environments to see increases in productivity.
A good way to mitigate the impact of the J-curve is to complete a value stream mapping (VSM) exercise to discover and anticipate the effect of bottlenecks. In a VSM exercise you look at a single change as it progresses from version control to production:
- Consider the various processes each change goes through, such as automated and manual testing, security review, change management, and release to production.
- Measure the total time for the change to go from version control to
released. For each process, measure the following:
- The actual elapsed time and the value-add time (the time during which work is actually being done) involved in executing the process end-to-end.
- The percentage of time that work is sent back because it was not done right the first time. This metric is known as percentage complete and accurate, or %C/A.
The purpose of the value stream mapping exercise is to help you find inefficiencies in your process. As a team, create a diagram of how you want the value stream to look in six months, and set aside team capacity to work on implementing this future state. Identify and remove obstacles that have a process with a long elapsed time compared to the value-add time or that have a poor %C/A.
It is usually necessary to tackle significant process and architecture redesign as part of implementing a deployment pipeline. Because the deployment pipeline goes from check-in to release, it connects multiple teams. It's essential to have representatives from all teams complete a value stream mapping exercise, and to agree on a common toolchain and processes (for example for deployment to testing and production environments) as part of your future state.
Implementing continuous delivery is a process of continuous, daily improvement work, guided by the outcomes that you want to achieve. Tools and patterns are valuable, but only in service to this essential improvement work.
Measuring continuous delivery
Ultimately, the goal of continuous delivery is to ensure that releases are performed in a low-risk way during normal business hours. The goal should be that nobody has to work outside of regular business hours to perform deployments or releases, so this is something that is important to measure.
How well you are doing at continuous delivery is reflected in the outcomes that you achieve. You can take the DORA DevOps quick check to see how you're doing with the key continuous delivery metrics:
- Short lead times for both regular and emergency changes, with a goal of using your regular process for emergency changes.
- Low change fail rates.
- Short time to restore service in the event of outages or service degradations.
- Release frequencies that ensure that high-priority features and bug fixes are released in a timely manner.
As discussed at the start of this document, implementing continuous delivery should also lead to lower levels of rework, reduced deployment pain, and less time spent doing rework and unplanned work.
- For links to other articles and resources, see the DevOps page.
- Learn more about continuous delivery in Martin Fowler's Software delivery guide.
- Read Value Stream Mapping: How to Visualize Work and Align Leadership for Organizational Transformation by Karen Martin and Mike Osterling.
- Explore our DevOps research program.
- Take the DevOps quick check to understand where you stand in comparison with the rest of the industry.