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49 lines
1.9 KiB
Markdown
49 lines
1.9 KiB
Markdown
# Checkout Strategy
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You can configure how Atlantis checks out the code from your pull request via
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the `--checkout-strategy` flag or the `ATLANTIS_CHECKOUT_STRATEGY` environment
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variable that get passed to the `atlantis server` command.
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Atlantis supports `branch` and `merge` strategies.
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## Branch
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If set to `branch` (the default), Atlantis will check out the source branch
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of the pull request.
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For example, given the following git history:
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If the pull request was asking to merge `branch` into `master`,
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Atlantis would check out `branch` at commit `C3`.
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## Merge
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The problem with the `branch` strategy, is that if users push branches that are
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out of date with `master`, then their `terraform plan` could be deleting
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some resources that were configured in the master branch.
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For example, in the above diagram if commits `C4` and `C5` have modified the
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terraform state and added new resources, then when Atlantis runs `terraform plan`
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at commit `C3`, because the code doesn't have the changes from `C4` and `C5`,
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Terraform will try to delete those resources.
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To fix this, users could merge `master` into their branch, *or* you can run
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Atlantis with `--checkout-strategy=merge`. With this strategy, Atlantis will
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try to perform a merge locally by:
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* Checking out the destination branch of the pull request (ex. `master`)
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* Locally performing a `git merge {source branch}`
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* Then running its Terraform commands
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In this example, the code that Atlantis would be operating on would look like:
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Where Atlantis is using its local commit `C6`.
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:::tip NOTE
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Atlantis doesn't actually commit this merge anywhere. It just uses it locally.
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:::
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:::warning
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Atlantis only performs this merge during the `terraform plan` phase. If another
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commit is pushed to `master` **after** Atlantis runs `plan`, nothing will happen.
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:::
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