When comparing CircleCI vs Jenkins, the Slant community recommends Jenkins for most people. In the question“What are the best continuous integration tools?” Jenkins is ranked 2nd while CircleCI is ranked 3rd. The most important reason people chose Jenkins is:
Jenkins is a free and open source continuous integration tool, while its source code is hosted on [GitHub](https://github.com/jenkinsci/jenkins/).
Ranked in these QuestionsQuestion Ranking
Pro Very fast parallel testing
Tests can be parallelized across multiple machines reducing test times drastically. They support up to 8-way parallelization. Additionally, CircleCI caches the build environment.
Pro Easy configuration with YAML
In most cases CircleCI automatically get settings from your code. When it fails, edit circle.yml.
Pro Quick setup
CircleCI excels with its setup process. All that's needed is a GitHub login and CircleCI automatically detects the settings for Ruby, Python, Node.js, Java and Clojure. The setup process is their most widely praised feature.
Pro Simple and intuitive GitHub integration
CircleCI can be connected to any project that is hosted on GitHub by logging in using the GitHub OAuth and adding the desired repository.
Whenever a new commit is pushed to GitHub, CircleCI runs the tests that have been already defined and if none of them fails, the build is deployed to the runtime environment.
Pro SSH support
Users can access the Virtual Machine via SSH and run commands.
Pro Clean, intuitive UI
Circle CI's web UI is clean and easy to use.
It gives all the information for a single build in a feed and gives the explanation for each step of the build, what it's doing and what the step is related to. On the top it displays author information and the time and date when the build was started and finished.
This is all done by giving only the most essential information without clogging the screen.
Pro Supports 8 languages and 16 databases
It als has support for: MySQL, MongoDB, PostgreSQL, Cassandra, Riak, Redis, SQLite, Solr, CouchDB, ElasticSearch, Neo4j, Couchbase, Lucene, Sphinx, ThriftDB, Memcache.
Pro Headless browser support
Alongside latest Chrome, Firefox and Webkit (installed using xvfb), CircleCi supports the use of Selenium, PhantomJS as well as tools like Capybara and Cucumber.
Pro Support for Queues
Support for RabbitMQ, Beanstalk and Resque through Redis.
Pro Supports Docker
CircleCI can continuously deliver Docker images to hosts that support Docker containers.
Pro Provides time taken for each step
With this information, it's easy to find out which line of the script is the bottleneck of the build process.
Pro Comprehensive cache dependencies
Can specify the cache dependencies on
- checksum "package.json"
For more details https://circleci.com/docs/2.0/caching/
Pro Intelligent notifications
CircleCI can notify via email, Hipchat, Campfire and more. And it does so only when necessary.
Pro Can test many code pushes concurrently
You can push multiple batches of code concurrently.
Pro Supports 10 Continuous Deployment solutions
Support for Heroku, AWS, Engine Yard, dotCloud, Fabric, Nodejitsu, AppFog, Capistrano, Rockspace, Joynet.
Integration with Heroku is solid with the ability to automatically deploy or merge branches.
CircleCI is also very flexible with the deployment arrangement allowing SSH key management, deployment freedom including directly to a PaaS, using Capistrano, Fabric, arbitrary bash commands, or by auto-merging to another branch, or packaging code up to S3.
Pro Free and open source
Jenkins is a free and open source continuous integration tool, while its source code is hosted on GitHub.
Pro Safe to store key environment variables
Self-hosting provides a safe location to store key environment variables since it is the user who is in charge of the server and environment where Jenkins is hosted.
Pro Highly customizable
Even though Jenkins is pretty functional and useful out of the box, there's a large plugin ecosystem from which the user can choose plugins to integrate into their Jenkins build. This is needed for when the user wants to extend any of the tool's features.
Pro A lot of resources and tutorials available
Jenkins has been in development since 2004 and is one of the most popular tools of its kind. This means that its technology is very mature and there is a lot of documentation and resources available for it.
Pro Multiple version control systems supported
Supports the most popular version control systems out of the box: SVN, Mercurial, and Git.
Pro Quantity of available Plugins
For most operations we need not reinvent the wheel, there are plugins already existing.
Pro Stable release line for users who want less changes
This is called the Jenkins Long-Term Support (LTS) version and helps to provide the most stable and assuring version of the Jenkins CI possible. Every 3 months, a version (which has been deemed the most reliable by the community) is chosen. After this, its branched, well-tested features are added (if they are missing), it is tested with the new features, bug fixes are then carried out if necessary, and from there it is released as the official Jenkins LTS version.
Pro Easy to get up and running
A Jenkins install is very simple and the user can have the service up and running within minutes. To install Jenkins, the command
java -jar jenkins.war is all that is needed - nothing more.
Pro User can source control their chain of automation
Starting with Jenkins 2.0, the pipeline capability, which has been available as a plugin before this version, has been built into Jenkins itself. This allows developers to describe their chain of automation in text form, which can be version controlled and put alongside the source tree.
The distributed builds in Jenkins work effectively, thanks to the Master and Slave capabilities.
Pro Cross-platform build support
Being a Java application it can be installed under any OS: Windows, Linux, and macOS. On the other hand, JNLP slaves also enriches the cross-platform build support for its agents.
Pro Self hosted
You stay in full control of your source code, build environment and deployment. No third party gets access to your source code or knows exactly how to build your software.
Pro Awards and recognition
Including InfoWorld Bossie Award (Best of Open Source Software Award) in 2011, and Received Geek Choice Award in 2014.
Pro Encryption of secrets
Thanks to JENKINS Credentials and Plugin.
Pro Multiple test environments for different runtime versions
They can be added easily under your Global Configuration.
Con Changes the environment without warning
Unless you count forum posts as a warning. A mysql upgrade caused days of debugging.
Con Does not cache docker images
The way to fake it is to save the image on disk, in the cache folder (it tars it), and restore it afterwards. But in tests it was slower than not caching.
Con Docker is way outdated on the VM provided
Currently (October 5th 2016), Docker installed on the VM is: 1.9.1-circleci-cp-workaround, build 517b158, and docker-compose is 1.5.2, build 7240ff3. docker-compose in particular is almost too old to be used.
Con High overhead
Unlike some of the simple and hosted alternatives, users need to host and setup Jenkins by themselves. This results in both a high initial setup time, as well as time sunk into maintenance over a project's duration.
Con Poor quality plug-ins that are difficult to combine
There have been several complaints by users regarding the quality of the plug-ins found in Jenkins' official plugin repo. A lot of plugins found in the default plugin directory are no longer actively maintained and as a result, they may be incompatible with later versions of Jenkins or other plugins.
Con Unstable and lack of plugin integration QA process
Jenkins without plugins is almost useless. All plugins are treated equal and published almost right away.
Because there is no process for testing Jenkins' integration, the overall Jenkins experience is not that great. Furthermore, Jenkins' core and plugins are released on a regular basis, all requiring instant restarts, meaning that updates appear more than once a day!