67 lines
2.9 KiB
Markdown
67 lines
2.9 KiB
Markdown
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---
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title: "About Terraform Runs in Atlas"
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---
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# About Terraform Runs in Atlas
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A "run" in Atlas represents the logical grouping of two Terraform steps - a
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"plan" and an "apply". The distinction between these two phases of a Terraform
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run are documented below.
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When a [new run is created](/help/terraform/runs/starting), Atlas automatically
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queues a Terraform plan. Because a plan does not change the state of
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infrastructure, it is safe to execute a plan multiple times without
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consequence. An apply executes the output of a plan and actively changes
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infrastructure. To prevent race conditions, Atlas will only execute one
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plan/apply at a time (plans for validating GitHub Pull Requests are allowed to
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happen concurrently, as they do not modify state). You can read more about
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Terraform plans and applies below.
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## Plan
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During the plan phase of a run, Atlas executes the command `terraform plan`.
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Terraform performs a refresh and then determines what actions are necessary to
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reach the desired state specified in the Terraform configuration files. A
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successful plan outputs an executable file that is securely stored in Atlas
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and may be used in the subsequent apply.
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Terraform plans in Atlas do not change the state of infrastructure, so it is
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safe to execute a plan multiple times. In fact, there are a number of components
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in Atlas that can trigger a Terraform plan. You can read more about this in the
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[starting runs](/help/terraform/runs/starting) section.
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## Apply
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During the apply phase of a run, Atlas executes the command `terraform apply`
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with the executable result of the prior Terraform plan. This phase **can change
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infrastructure** by applying the changes required to reach the desired state
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specified in the Terraform configuration file.
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While Terraform plans are safe to run multiple times, Terraform applies often
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change active infrastructure. Because of this, the default behavior for Atlas
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is to require user confirmation as part of the
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[Terraform run execution](/help/terraform/runs/how-runs-execute). Upon
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user confirmation, Atlas will queue and execute the Terraform apply. It is also
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possible to configure Atlas to
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[automatically apply](/help/terraform/runs/automatic-applies), but this option is
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disabled by default.
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## Environment Locking
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During run execution, Atlas will lock the environment to prevent other plans
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and applies from executing simultaneously. When the run completes, the next
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pending run, if any, will be started.
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An administrator of the environment can also manually lock the environment, for
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example during a maintenance period.
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You can see the lock status of an environment, and lock/unlock the environment
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by visiting that environment's settings page.
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## Notifications
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To receive alerts when user confirmation is needed or for any other phase of the
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run process, you can
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[enable run notifications](/help/terraform/runs/notifications) for your
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organization or environment.
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