By default, Terraform stores state locally in a file named
When working with Terraform in a team, use of a local file makes Terraform
usage complicated because each user must make sure they always have the latest
state data before running Terraform and make sure that nobody else runs
Terraform at the same time.
With remote state, Terraform writes the state data to a remote data store, which can then be shared between all members of a team. Terraform supports storing state in Terraform Cloud, HashiCorp Consul, Amazon S3, Azure Blob Storage, Google Cloud Storage, Alibaba Cloud OSS, and more.
Remote state is implemented by a backend or by Terraform Cloud, both of which you can configure in your configuration's root module.
Remote state allows you to share output values with other configurations. This allows your infrastructure to be decomposed into smaller components.
Put another way, remote state also allows teams to share infrastructure resources in a read-only way without relying on any additional configuration store.
For example, a core infrastructure team can handle building the core machines, networking, etc. and can expose some information to other teams to run their own infrastructure. As a more specific example with AWS: you can expose things such as VPC IDs, subnets, NAT instance IDs, etc. through remote state and have other Terraform states consume that.
For example usage, see
terraform_remote_state data source.
While remote state can be a convenient, built-in mechanism for sharing data
between configurations, you may prefer to use more general stores to
pass settings both to other configurations and to other consumers. For example,
if your environment has HashiCorp Consul then you
can have one Terraform configuration that writes to Consul using
consul_key_prefix and then
another that consumes those values using
consul_keys data source.
For fully-featured remote backends, Terraform can also use state locking to prevent concurrent runs of Terraform against the same state.
Terraform Cloud by HashiCorp is a commercial offering that supports an even stronger locking concept that can also detect attempts to create a new plan when an existing plan is already awaiting approval, by queuing Terraform operations in a central location. This allows teams to more easily coordinate and communicate about changes to infrastructure.