Continuous Integration vs. Continuous Delivery vs. Continuous Deployment
Before we start to understand various DevOps concepts we need to figure out what “continuous” means in software. Basically, the term “continuity” refers to software changes that occur throughout the software development process.
And of course, there is some trickery in the term “continuous”.
In fact, after the implementation of the functionality, it may take some time before the code goes into production, but this time is still much less than it was before the DevOps appearance.
Continuous Integration (CI), Continuous Delivery (CD), and Continuous Deployment (CD) are integral parts and foundation of the DevOps approach to software development and upgrading, which implies continuous, pipeline testing, build, delivery and deployment of updates. It is possible to both separate use the components of this approach (CI or CI + CD), and their sequential use within a single process (CI + CD + CD), since the goal pursued by CI/CD is to get high-quality code in a short time.
When an organization is constantly changing and becoming the norm, software development cycles become more frequent. By using CI/CD processes in software development, more frequent updates can be released on an ongoing basis without loss of quality.
The ideal process looks something like this:
⇒ the developer pushes the code to the central storage;
⇒ on the continuous integration server, changes are merged with the main code, unit tests are implemented and everything is uploaded to the staging environment;
⇒ QA engineers test the application in the staging environment;
⇒ then everything is checked for getting into production;
⇒ deployment to production.
CONTINUOUS INTEGRATION
Continuous Integration is a software development practice that requires developers to upload code to central storage on a regular basis, several times a day.
Each code update is then validated with automated tests, allowing the development team to identify problems at an early stage. This allows teams to spend less time looking for problems in the code and more time creating new features.
Integration process
Developers write code in their own separate branches and then push the results to central storage. Automated unit and integration tests are implemented — based on their results errors and other code quality issues are revealed. After successfully passing the automated tests, developers can view the changes in the shared code branch and create pull requests. This mechanism allows developers to directly review and propose changes in the main branch of the code created by other developers working on the project.
Once the review process is complete and the new code is merged with the main branch, the cycles of further review and bug fixing continue on the basis of the integrated main branch. This often happens several times a day, especially in a large team where everyone is working on many smaller tasks. In this case, everyone is working with the same version of the code. The divergence of code versions and the related issues that may arise due to the desynchronization of developers’ actions are significantly reduced or disappear.
Continuous Integration: how everything works
It remains to figure out how and where Continuous Integration carries out such a huge amount of work, and even so quickly. The system itself does not collect or test the code. This is done by other machines — computers or virtual servers, so-called “agents”.
➢ Continuous Integration systems have a server and a client. The server is directly the part that is available to the development team, a convenient interface where they can evaluate how successful the build and tests were.
➢ The “client” is installed on “agent” machines or virtual servers.
➢ When the server receives a command, it searches for a free “agent” and gives it instructions on what to do, what tests to conduct.
➢ The “agent” carries out all this, generates the results and sends them back to the server.
➢ The server formalizes everything and shows it to those who need it or sends them letters.
It is important that the user always see which machine has done all the work at any given moment. The user can choose himself the “agent” for the build and tests.
Pros of Continuous Integration
⇒ You can identify problems at an early stage and fix them before merging new code into the main branch.
⇒ Communication between the team is improved due to better visualization.
⇒ Bugs can be found faster.
⇒ No need to sit and wait for the code test to finish. You can work on a new piece.
⇒ A lot of feedback on the changes. This will help improve the product.
Systems for Continuous Integration
As we mentioned above, there are quite a few systems for continuous integration. Consider the features of those that are used most often.
TeamCity — this service supports a lot of powerful functionality. There is a free version for small projects. The service has clear integration with control systems, is highly reliable, and does not depend on the launch of the build. You can run commands remotely.
Jenkins — is an open-source Java tool. You can test the code in real-time, generate reports on individual changes in the codebase. It is suitable for quick markings and fixes of errors and bugs in the code. Jenkins is easy to set up and is available on Linux, Mac and Windows.
Codeship — is a continuous integration tool that automates development and deployment. It allows you to customize the access levels of team members for each project. There is a debugging function right from the continuous integration environment and it also has a convenient toolbar.
Travis — is a web resource. It can be used free of charge for open-source projects and supports quite a few programming languages, including Node and PHP. Easily customizable, it integrates with Slack, HipChat, email and uses virtual machines for a build. It is possible to run parallel testing.
Additional reading: What Are NoSQL Databases and Why Enterprises Rely on NoSQL?
CONTINUOUS DELIVERY
Continuous Delivery is a process in which changes to the code automatically lead to a new build, testing, and preparation for release. As a result, the created software can be sent to production at any time.
Continuously integrated new pieces of code are further tested for performance and functionality until they are approved by developer reviewers for inclusion in the main branch of the code. For the reliable and smooth functioning of the continuous delivery process, the foundation in the form of an efficient continuous integration process is very important. When implemented correctly, developers will always have a ready-to-deploy version of the build that has gone through a standardized testing process.
The process begins when the developer pushes the written code to the storage and ends when testing is complete so that the code is fully ready for deployment in a production environment. If any errors or bugs occur during automated testing, the CI tool will automatically notify the developer via email or SMS.
Continuous delivery usually includes a staging environment namely an environment that is as close to production as possible but without actual data, where changes are made manually before the production release. The decision on readiness and production is more a business decision than an IT decision.
Benefits of CI/CD
– Reducing risks. Some tasks such as testing the application in different versions of different browsers can be automated to reduce the risk of errors.
– Fast time to market. Errors in the code are detected at an earlier stage and can be quickly eliminated, which leads to an increase in the speed of delivery.
– One source. All members of the development team use the same central storage to write their code. It is always known what changes were made and by whom.
– Increased code coverage. The CI server checks for test coverage for each build. Wherever you add new lines of code without the required test classes, the server will throw an error as there is not enough code coverage. Accordingly, developers will be forced to work to increase coverage at lower tiers so that there are no problems with deployment.
– Quality. CI helps QA engineers spend 50% less time from the total project time by running nominal integration tests looking for bugs and other issues. This allows the QA team to dive deeper into issues, develop more test cases, and ultimately achieve an overall improvement in results.
– Reducing the backlog. CI/CD reduces the number of small defects in the backlog as these are already known in advance and fixed before release.
– Customer Satisfaction. Continuous delivery and deployment allow you to receive real-time feedback, as well as promptly correct team miscalculations. With this approach, new product development will be more advanced and more in line with the expectations of the end-user.
– Reduced team conflicts. The CI practice ensures that code written by multiple developers in different locations is always integrated into the central storage. This avoids the chaos and problems caused by code updates.
CONTINUOUS DEPLOYMENT
Continuous Deployment is very similar to continuous delivery. The only difference between the two is that with continuous deployment, any added piece of code that passes all the automated testing steps will be immediately released to production.
Continuous Deployment does not require any additional manual testing in a staging environment, as automated testing is performed in the preceding phases. Both continuous delivery and continuous deployment rely heavily on infrastructure readiness and application monitoring to detect any issues as soon as possible that were not identified in the feedback loops during the testing phases, since there is no manual verification involved.
CONCLUSION
To sum up:
CI is performed immediately after the developer checks in. While in Continuous Delivery, developed code is continuously delivered until the programmer considers it is ready to ship and in Continuous Deployment, developers deploy the code directly to the production stage when it is developed.
Simply put, CI is the process of integrating code into a mainline codebase. CD is about the processes that have to happen after code is integrated for app changes to be delivered to users. Those processes involve testing, staging and deploying code.
Moving to continuous integration and continuous delivery significantly changes the software development process, allowing it to be simplified, thereby helping to create a stable, safe and quality product.
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Written by: Liza Hazevych, Marketing Manager at DevCom.
