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Backends
Each Terraform configuration can specify a backend, which defines where and how operations are performed, where state snapshots are stored, etc.
The rest of this page introduces the concept of backends; the other pages in this section document how to configure and use backends.
- Backend Configuration documents the form
of a
backendblock, which selects and configures a backend for a Terraform configuration. - This section also includes a page for each of Terraform's built-in backends, documenting its behavior and available settings. See the navigation sidebar for a complete list.
Recommended Backends
- If you are still learning how to use Terraform, we recommend using the default
localbackend, which requires no configuration. - If you and your team are using Terraform to manage meaningful infrastructure,
we recommend using the
remotebackend with Terraform Cloud or Terraform Enterprise.
Where Backends are Used
Backend configuration is only used by Terraform CLI. Terraform Cloud and Terraform Enterprise always use their own state storage when performing Terraform runs, so they ignore any backend block in the configuration.
But since it's common to
use Terraform CLI alongside Terraform Cloud
(and since certain state operations, like tainting,
can only be performed on the CLI), we recommend that Terraform Cloud users
include a backend block in their configurations and configure the remote
backend to use the relevant Terraform Cloud workspace(s).
Where Backends Come From
Terraform includes a built-in selection of backends; this selection has changed over time, but does not change very often.
The built-in backends are the only backends. You cannot load additional backends as plugins.
What Backends Do
There are two areas of Terraform's behavior that are determined by the backend:
- Where state is stored.
- Where operations are performed.
State
Terraform uses persistent state data to keep track of the resources it manages. Since it needs the state in order to know which real-world infrastructure objects correspond to the resources in a configuration, everyone working with a given collection of infrastructure resources must be able to access the same state data.
The local backend stores state as a local file on disk, but every other
backend stores state in a remote service of some kind, which allows multiple
people to access it. Accessing state in a remote service generally requires some
kind of access credentials, since state data contains extremely sensitive
information.
Some backends act like plain "remote disks" for state files; others support locking the state while operations are being performed, which helps prevent conflicts and inconsistencies.
Operations
"Operations" refers to performing API requests against infrastructure services
in order to create, read, update, or destroy resources. Not every terraform
subcommand performs API operations; many of them only operate on state data.
Only two backends actually perform operations: local and remote.
The local backend performs API operations directly from the machine where the
terraform command is run. Whenever you use a backend other than local or
remote, Terraform uses the local backend for operations; it only uses the
configured backend for state storage.
The remote backend can perform API operations remotely, using Terraform Cloud
or Terraform Enterprise. When running remote operations, the local terraform
command displays the output of the remote actions as though they were being
performed locally, but only the remote system requires cloud credentials or
network access to the resources being managed.
Remote operations are optional for the remote backend; the settings for the
target Terraform Cloud workspace determine whether operations run remotely or
locally. If local operations are configured, Terraform uses the remote backend
for state and the local backend for operations, like with the other state
backends.