github.com/hugorut/terraform@v1.1.3/website/docs/language/state/purpose.mdx (about) 1 --- 2 page_title: State 3 description: >- 4 Terraform must store state about your managed infrastructure and 5 configuration. This state is used by Terraform to map real world resources to 6 your configuration, keep track of metadata, and to improve performance for 7 large infrastructures. 8 --- 9 10 # Purpose of Terraform State 11 12 State is a necessary requirement for Terraform to function. It is often 13 asked if it is possible for Terraform to work without state, or for Terraform 14 to not use state and just inspect cloud resources on every run. This page 15 will help explain why Terraform state is required. 16 17 As you'll see from the reasons below, state is required. And in the scenarios 18 where Terraform may be able to get away without state, doing so would require 19 shifting massive amounts of complexity from one place (state) to another place 20 (the replacement concept). 21 22 ## Mapping to the Real World 23 24 Terraform requires some sort of database to map Terraform config to the real 25 world. When you have a resource `resource "aws_instance" "foo"` in your 26 configuration, Terraform uses this map to know that instance `i-abcd1234` 27 is represented by that resource. 28 29 For some providers like AWS, Terraform could theoretically use something like 30 AWS tags. Early prototypes of Terraform actually had no state files and used 31 this method. However, we quickly ran into problems. The first major issue was 32 a simple one: not all resources support tags, and not all cloud providers 33 support tags. 34 35 Therefore, for mapping configuration to resources in the real world, 36 Terraform uses its own state structure. 37 38 Terraform expects that each remote object is bound to only one resource 39 instance, which is normally guaranteed by Terraform being responsible for 40 creating the objects and recording their identities in the state. If you 41 instead import objects that were created outside of Terraform, you'll need 42 to check yourself that each distinct object is imported to only one resource 43 instance. 44 45 If one remote object is bound to two or more resource instances then Terraform 46 may take unexpected actions against those objects, because the mapping from 47 configuration to the remote object state has become ambiguous. 48 49 ## Metadata 50 51 Alongside the mappings between resources and remote objects, Terraform must 52 also track metadata such as resource dependencies. 53 54 Terraform typically uses the configuration to determine dependency order. 55 However, when you delete a resource from a Terraform configuration, Terraform 56 must know how to delete that resource. Terraform can see that a mapping exists 57 for a resource not in your configuration and plan to destroy. However, since 58 the configuration no longer exists, the order cannot be determined from the 59 configuration alone. 60 61 To ensure correct operation, Terraform retains a copy of the most recent set 62 of dependencies within the state. Now Terraform can still determine the correct 63 order for destruction from the state when you delete one or more items from 64 the configuration. 65 66 One way to avoid this would be for Terraform to know a required ordering 67 between resource types. For example, Terraform could know that servers must be 68 deleted before the subnets they are a part of. The complexity for this approach 69 quickly explodes, however: in addition to Terraform having to understand the 70 ordering semantics of every resource for every cloud, Terraform must also 71 understand the ordering _across providers_. 72 73 Terraform also stores other metadata for similar reasons, such as a pointer 74 to the provider configuration that was most recently used with the resource 75 in situations where multiple aliased providers are present. 76 77 ## Performance 78 79 In addition to basic mapping, Terraform stores a cache of the attribute 80 values for all resources in the state. This is the most optional feature of 81 Terraform state and is done only as a performance improvement. 82 83 When running a `terraform plan`, Terraform must know the current state of 84 resources in order to effectively determine the changes that it needs to make 85 to reach your desired configuration. 86 87 For small infrastructures, Terraform can query your providers and sync the 88 latest attributes from all your resources. This is the default behavior 89 of Terraform: for every plan and apply, Terraform will sync all resources in 90 your state. 91 92 For larger infrastructures, querying every resource is too slow. Many cloud 93 providers do not provide APIs to query multiple resources at once, and the 94 round trip time for each resource is hundreds of milliseconds. On top of this, 95 cloud providers almost always have API rate limiting so Terraform can only 96 request a certain number of resources in a period of time. Larger users 97 of Terraform make heavy use of the `-refresh=false` flag as well as the 98 `-target` flag in order to work around this. In these scenarios, the cached 99 state is treated as the record of truth. 100 101 ## Syncing 102 103 In the default configuration, Terraform stores the state in a file in the 104 current working directory where Terraform was run. This is okay for getting 105 started, but when using Terraform in a team it is important for everyone 106 to be working with the same state so that operations will be applied to the 107 same remote objects. 108 109 [Remote state](/language/state/remote) is the recommended solution 110 to this problem. With a fully-featured state backend, Terraform can use 111 remote locking as a measure to avoid two or more different users accidentally 112 running Terraform at the same time, and thus ensure that each Terraform run 113 begins with the most recent updated state.