Add blog post about moving Rust's CI to GitHub Actions

posts/inside-rust/2020-07-23-rust-ci-is-moving-to-github-actions.md

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+---
+layout: post
+title: "Rust's CI is moving to GitHub Actions"
+author: Pietro Albini
+team: the infrastructure team <https://www.rust-lang.org/governance/teams/operations#infra>
+---
+
+The Rust Infrastructure Team is happy to announce that, as part of the
+[evaluation we started last year][eval], most of Rust’s CI is moving to GitHub
+Actions! While we don’t expect the change to have any impact on our users, the
+switch will considerably improve the experience for compiler contributors.
+
+One of the major pain points for compiler contributors over the past few years
+has been waiting for PRs to be merged. We value having an always-green master
+branch, and to ensure that, we test and merge just one PR at a time, with the
+other approved ones [waiting in the queue][homu]. Our CI is extensive too, with
+57 machines building and testing the compiler across all the platforms we
+support. On our previous system, each of those builders took between three to
+four hours to finish. Combined with testing one PR at a time, this often causes
+PRs to wait in the queue for days before being tested.
+
+Making the CI setup faster is a permanent goal of the Infrastructure Team, and
+GitHub Actions provided us with a great opportunity to improve landing time:
+GitHub offered to sponsor a fully managed, private pool of 8-core VMs to run
+our builds on, which is a big improvement compared to the 2-core VMs we were
+previously using. GitHub Actions also provides most of the features we loved
+about Azure Pipelines while being integrated with GitHub’s permissions and UI,
+which made the switch even more fruitful.
+
+As of July 22nd, all the CI builds for the [rust-lang/rust] repository except
+for macOS builds are running exclusively on GitHub Actions! We’re still running
+macOS builds on Azure Pipelines for the time being, as we’re waiting on GitHub
+to fix [issue #71988][71988], but we hope to move them to GitHub Actions soon.
+
+We’d like to thank GitHub for sponsoring our CI builders and Microsoft for the
+Azure Pipelines capacity we used over the past year.
+
+[eval]: https://blog.rust-lang.org/inside-rust/2019/11/14/evaluating-github-actions.html
+[homu]: https://bors.rust-lang.org/queue/rust
+[rust-lang/rust]: https://github.com/rust-lang/rust
+[71988]: https://github.com/rust-lang/rust/issues/71988