When comparing TeamCity vs GitLab CI, the Slant community recommends TeamCity for most people. In the question“What are the best continuous integration tools?” TeamCity is ranked 1st while GitLab CI is ranked 2nd. The most important reason people chose TeamCity is:
TeamCity has different installation packages for different operating systems. All the user needs to do is download the correct one and run it.
Specs
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Pros
Pro Easy installation
TeamCity has different installation packages for different operating systems. All the user needs to do is download the correct one and run it.
Pro Cross-platform build support
The fact that it is based on Java does not hinder TeamCity's ability to support different build environments. TeamCity in fact supports a large number of languages and tools for each of those languages (build runners and test frameworks).
Some of the languages/platforms that are supported include: Ruby, .NET, Java.
Pro Brilliant interface
The user interface of TeamCity is clear, well thought out and the dashboard is highly customizable.
Pro Supports build chains
The user can easily compose dependencies between builds by adding snapshot and artifact dependencies, all on the one screen. All output of upstream builds is available to downstream builds. Triggering sets off the entire build chain and supports re-running of the portions of the chain that failed.
Pro Well documented
Pro Extensible
TeamCity offers well defined APIs for extending, as well as a REST interface.
Pro Testing support
TeamCity supports both MSTest and NUnit (which is open source) to run tests.
Pro Best choice for .NET
Seems to be the best choice for .NET applications, but to be honest: if you stray from the default settings you will be in a lot of pain most of the time.
Pro File based configuration
All build setup are stored in .gitlab-ci.yml file, which is versioned and stored in the project. Like Travis do.
Pro Free and open source
All of GitLab CI's code is open source and under the MIT license.
Pro Parallel builds lessen test times
Tests are parallelized across multiple machines in order to reduce test times considerably.
Pro Docker intergration
Good integration with Docker.
Pro Highly scalable
The tests of GitLab CI run parallel to each other and are distributed on different machines. Developers can add as many machines as they want or need, making GitLab CI highly scalable to the development team's needs.
Pro Quick setup for projects hosted on GitLab
Since it uses the GitLab API for setting up hooks, the setup of GitLab CI for projects hosted on GitLab can be done in one click.
Pro Kubernetes integration
Easy to test and deploy on Kubernetes.
Cons
Con Expensive
TeamCity has a free tier which includes a maximum of 100 build configurations and up to 3 build agents. If you want to add 10 more configurations and 1 more agent, it will cost $299; unless you choose to buy an enterprise license which starts at $1999.
Con Poor quality plugins
At least some of them do not work, probably because they're not updated to more recent TeamCity versions.
Con Inter-branch merges trigger emails to unrelated committers
Whenever an inter-branch merge occurs, TeamCity pulls up the first parent of the merge commit and sends them an e-mail. However, this sort of information would be more useful to the merge author.
Con Not lightweight
Not a lightweight solution, demanding and memory hungry.
Con Cost
Larger projects will need upgraded version
Con Security risks
Con Windows not supported
No Windows support, but it's possible to use a Bitnami stack.