CircleCI vs TeamCity

• Multiple builds can be run at the same time in parallel.
• The CircleCI web interface (UI/UX) is very easy to understand and use.
• Easy Configuration to learn and use. Just a single configuration YAML file.
• Many integrations. We use the GItHub, Slack, and DataDog integrations.

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• Fully customizable build process. Each step of the build process can be parameterized and customized to address specific needs of particular applications. This allowed us to easily convert from a custom VM-based environment to our current Docker-based environment.
• Manages large numbers of build agents seamlessly. This allows us to run multiple builds on many different applications in a most efficient manner.
• Build steps can be managed in an arbitrary manner, allowing some parts of the process to proceed in parallel while restricting others to depend on completion of all relevant steps.

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• The "phases" their config file uses to separate out options seem very arbitrary and are not very helpful for organizing your config file
• No way that I know of to configure which version of MongoDB you use. You have to write your own shell script to download and start MongoDB if you want a specific version.
• Hard to access build artifacts in the UI

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• Reading build output logs can be a pain at times, as they aren't really parsed; just long lines of output.
• When you have multiple projects and branches, determining what is currently building, what is pending, and what has failed can be difficult.

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• It has eased the burden of standardizing our testing and deployment, making onboarding new developers much faster, and having to fix deployment mistakes much less often.
• It allows us to focus our process around the GitHub workflow, ignoring the details of whatever environment the thing we're working on is actually hosted in. This saves us time.

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• It has drastically improved the turnaround time for building and deploying projects to Production
• The build process can be augmented by adding build servers quickly
• In my opinion the licensing cost is not expensive at least for small to medium enterprises, although I haven't looked in detail into how it changes when you move up.

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