terraform/backend/backend.go

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// Package backend provides interfaces that the CLI uses to interact with
// Terraform. A backend provides the abstraction that allows the same CLI
// to simultaneously support both local and remote operations for seamlessly
// using Terraform in a team environment.
package backend
import (
"context"
"errors"
"github.com/hashicorp/terraform/config/module"
"github.com/hashicorp/terraform/state"
"github.com/hashicorp/terraform/terraform"
)
const DefaultStateName = "default"
// Error value to return when a named state operation isn't supported
var ErrNamedStatesNotSupported = errors.New("named states not supported")
// Backend is the minimal interface that must be implemented to enable Terraform.
type Backend interface {
// Ask for input and configure the backend. Similar to
// terraform.ResourceProvider.
Input(terraform.UIInput, *terraform.ResourceConfig) (*terraform.ResourceConfig, error)
Validate(*terraform.ResourceConfig) ([]string, []error)
Configure(*terraform.ResourceConfig) error
// State returns the current state for this environment. This state may
// not be loaded locally: the proper APIs should be called on state.State
// to load the state. If the state.State is a state.Locker, it's up to the
// caller to call Lock and Unlock as needed.
//
// If the named state doesn't exist it will be created. The "default" state
// is always assumed to exist.
State(name string) (state.State, error)
// DeleteState removes the named state if it exists. It is an error
// to delete the default state.
//
// DeleteState does not prevent deleting a state that is in use. It is the
// responsibility of the caller to hold a Lock on the state when calling
// this method.
DeleteState(name string) error
// States returns a list of configured named states.
States() ([]string, error)
}
// Enhanced implements additional behavior on top of a normal backend.
//
// Enhanced backends allow customizing the behavior of Terraform operations.
// This allows Terraform to potentially run operations remotely, load
// configurations from external sources, etc.
type Enhanced interface {
Backend
// Operation performs a Terraform operation such as refresh, plan, apply.
// It is up to the implementation to determine what "performing" means.
// This DOES NOT BLOCK. The context returned as part of RunningOperation
// should be used to block for completion.
// If the state used in the operation can be locked, it is the
// responsibility of the Backend to lock the state for the duration of the
// running operation.
Operation(context.Context, *Operation) (*RunningOperation, error)
}
// Local implements additional behavior on a Backend that allows local
// operations in addition to remote operations.
//
// This enables more behaviors of Terraform that require more data such
// as `console`, `import`, `graph`. These require direct access to
// configurations, variables, and more. Not all backends may support this
// so we separate it out into its own optional interface.
type Local interface {
// Context returns a runnable terraform Context. The operation parameter
// doesn't need a Type set but it needs other options set such as Module.
Context(*Operation) (*terraform.Context, state.State, error)
}
// An operation represents an operation for Terraform to execute.
//
// Note that not all fields are supported by all backends and can result
// in an error if set. All backend implementations should show user-friendly
// errors explaining any incorrectly set values. For example, the local
// backend doesn't support a PlanId being set.
//
// The operation options are purposely designed to have maximal compatibility
// between Terraform and Terraform Servers (a commercial product offered by
// HashiCorp). Therefore, it isn't expected that other implementation support
// every possible option. The struct here is generalized in order to allow
// even partial implementations to exist in the open, without walling off
// remote functionality 100% behind a commercial wall. Anyone can implement
// against this interface and have Terraform interact with it just as it
// would with HashiCorp-provided Terraform Servers.
type Operation struct {
// Type is the operation to perform.
Type OperationType
// PlanId is an opaque value that backends can use to execute a specific
// plan for an apply operation.
//
// PlanOutBackend is the backend to store with the plan. This is the
// backend that will be used when applying the plan.
PlanId string
PlanRefresh bool // PlanRefresh will do a refresh before a plan
PlanOutPath string // PlanOutPath is the path to save the plan
PlanOutBackend *terraform.BackendState
// Module settings specify the root module to use for operations.
Module *module.Tree
// Plan is a plan that was passed as an argument. This is valid for
// plan and apply arguments but may not work for all backends.
Plan *terraform.Plan
// The options below are more self-explanatory and affect the runtime
// behavior of the operation.
Destroy bool
Targets []string
Variables map[string]interface{}
// Input/output/control options.
UIIn terraform.UIInput
UIOut terraform.UIOutput
// If LockState is true, the Operation must Lock any
// state.Lockers for its duration, and Unlock when complete.
LockState bool
// Environment is the named state that should be loaded from the Backend.
Environment string
}
// RunningOperation is the result of starting an operation.
type RunningOperation struct {
// Context should be used to track Done and Err for errors.
//
// For implementers of a backend, this context should not wrap the
// passed in context. Otherwise, canceling the parent context will
// immediately mark this context as "done" but those aren't the semantics
// we want: we want this context to be done only when the operation itself
// is fully done.
context.Context
// Err is the error of the operation. This is populated after
// the operation has completed.
Err error
// PlanEmpty is populated after a Plan operation completes without error
// to note whether a plan is empty or has changes.
PlanEmpty bool
// State is the final state after the operation completed. Persisting
// this state is managed by the backend. This should only be read
// after the operation completes to avoid read/write races.
State *terraform.State
}