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backend.go
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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"
"io/ioutil"
"log"
"os"
"github.com/hashicorp/terraform/internal/addrs"
"github.com/hashicorp/terraform/internal/command/clistate"
"github.com/hashicorp/terraform/internal/command/views"
"github.com/hashicorp/terraform/internal/configs"
"github.com/hashicorp/terraform/internal/configs/configload"
"github.com/hashicorp/terraform/internal/configs/configschema"
"github.com/hashicorp/terraform/internal/depsfile"
"github.com/hashicorp/terraform/internal/plans"
"github.com/hashicorp/terraform/internal/plans/planfile"
"github.com/hashicorp/terraform/internal/states"
"github.com/hashicorp/terraform/internal/states/statemgr"
"github.com/hashicorp/terraform/internal/terraform"
"github.com/hashicorp/terraform/internal/tfdiags"
"github.com/mitchellh/go-homedir"
"github.com/zclconf/go-cty/cty"
)
// DefaultStateName is the name of the default, initial state that every
// backend must have. This state cannot be deleted.
const DefaultStateName = "default"
var (
// ErrDefaultWorkspaceNotSupported is returned when an operation does not
// support using the default workspace, but requires a named workspace to
// be selected.
ErrDefaultWorkspaceNotSupported = errors.New("default workspace not supported\n" +
"You can create a new workspace with the \"workspace new\" command.")
// ErrWorkspacesNotSupported is an error returned when a caller attempts
// to perform an operation on a workspace other than "default" for a
// backend that doesn't support multiple workspaces.
//
// The caller can detect this to do special fallback behavior or produce
// a specific, helpful error message.
ErrWorkspacesNotSupported = errors.New("workspaces not supported")
)
// InitFn is used to initialize a new backend.
type InitFn func() Backend
// Backend is the minimal interface that must be implemented to enable Terraform.
type Backend interface {
// ConfigSchema returns a description of the expected configuration
// structure for the receiving backend.
//
// This method does not have any side-effects for the backend and can
// be safely used before configuring.
ConfigSchema() *configschema.Block
// PrepareConfig checks the validity of the values in the given
// configuration, and inserts any missing defaults, assuming that its
// structure has already been validated per the schema returned by
// ConfigSchema.
//
// This method does not have any side-effects for the backend and can
// be safely used before configuring. It also does not consult any
// external data such as environment variables, disk files, etc. Validation
// that requires such external data should be deferred until the
// Configure call.
//
// If error diagnostics are returned then the configuration is not valid
// and must not subsequently be passed to the Configure method.
//
// This method may return configuration-contextual diagnostics such
// as tfdiags.AttributeValue, and so the caller should provide the
// necessary context via the diags.InConfigBody method before returning
// diagnostics to the user.
PrepareConfig(cty.Value) (cty.Value, tfdiags.Diagnostics)
// Configure uses the provided configuration to set configuration fields
// within the backend.
//
// The given configuration is assumed to have already been validated
// against the schema returned by ConfigSchema and passed validation
// via PrepareConfig.
//
// This method may be called only once per backend instance, and must be
// called before all other methods except where otherwise stated.
//
// If error diagnostics are returned, the internal state of the instance
// is undefined and no other methods may be called.
Configure(cty.Value) tfdiags.Diagnostics
// StateMgr returns the state manager for the given workspace name.
//
// If the returned state manager also implements statemgr.Locker then
// it's the caller's responsibility to call Lock and Unlock as appropriate.
//
// If the named workspace doesn't exist, or if it has no state, it will
// be created either immediately on this call or the first time
// PersistState is called, depending on the state manager implementation.
StateMgr(workspace string) (statemgr.Full, error)
// DeleteWorkspace removes the workspace with the given name if it exists.
//
// DeleteWorkspace cannot prevent deleting a state that is in use. It is
// the responsibility of the caller to hold a Lock for the state manager
// belonging to this workspace before calling this method.
DeleteWorkspace(name string) error
// States returns a list of the names of all of the workspaces that exist
// in this backend.
Workspaces() ([]string, error)
}
// Enhanced implements additional behavior on top of a normal backend.
//
// 'Enhanced' backends are an implementation detail only, and are no longer reflected as an external
// 'feature' of backends. In other words, backends refer to plugins for remote state snapshot
// storage only, and the Enhanced interface here is a necessary vestige of the 'local' and
// remote/cloud backends only.
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 {
// LocalRun uses information in the Operation to prepare a set of objects
// needed to start running that operation.
//
// The operation doesn't need a Type set, but it needs various other
// options set. This is a rather odd API that tries to treat all
// operations as the same when they really aren't; see the local and remote
// backend's implementations of this to understand what this actually
// does, because this operation has no well-defined contract aside from
// "whatever it already does".
LocalRun(*Operation) (*LocalRun, statemgr.Full, tfdiags.Diagnostics)
}
// LocalRun represents the assortment of objects that we can collect or
// calculate from an Operation object, which we can then use for local
// operations.
//
// The operation methods on terraform.Context (Plan, Apply, Import, etc) each
// generate new artifacts which supersede parts of the LocalRun object that
// started the operation, so callers should be careful to use those subsequent
// artifacts instead of the fields of LocalRun where appropriate. The LocalRun
// data intentionally doesn't update as a result of calling methods on Context,
// in order to make data flow explicit.
//
// This type is a weird architectural wart resulting from the overly-general
// way our backend API models operations, whereby we behave as if all
// Terraform operations have the same inputs and outputs even though they
// are actually all rather different. The exact meaning of the fields in
// this type therefore vary depending on which OperationType was passed to
// Local.Context in order to create an object of this type.
type LocalRun struct {
// Core is an already-initialized Terraform Core context, ready to be
// used to run operations such as Plan and Apply.
Core *terraform.Context
// Config is the configuration we're working with, which typically comes
// from either config files directly on local disk (when we're creating
// a plan, or similar) or from a snapshot embedded in a plan file
// (when we're applying a saved plan).
Config *configs.Config
// InputState is the state that should be used for whatever is the first
// method call to a context created with CoreOpts. When creating a plan
// this will be the previous run state, but when applying a saved plan
// this will be the prior state recorded in that plan.
InputState *states.State
// PlanOpts are options to pass to a Plan or Plan-like operation.
//
// This is nil when we're applying a saved plan, because the plan itself
// contains enough information about its options to apply it.
PlanOpts *terraform.PlanOpts
// Plan is a plan loaded from a saved plan file, if our operation is to
// apply that saved plan.
//
// This is nil when we're not applying a saved plan.
Plan *plans.Plan
}
// 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 *plans.Backend
// ConfigDir is the path to the directory containing the configuration's
// root module.
ConfigDir string
// ConfigLoader is a configuration loader that can be used to load
// configuration from ConfigDir.
ConfigLoader *configload.Loader
// DependencyLocks represents the locked dependencies associated with
// the configuration directory given in ConfigDir.
//
// Note that if field PlanFile is set then the plan file should contain
// its own dependency locks. The backend is responsible for correctly
// selecting between these two sets of locks depending on whether it
// will be using ConfigDir or PlanFile to get the configuration for
// this operation.
DependencyLocks *depsfile.Locks
// Hooks can be used to perform actions triggered by various events during
// the operation's lifecycle.
Hooks []terraform.Hook
// 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.
PlanFile *planfile.Reader
// The options below are more self-explanatory and affect the runtime
// behavior of the operation.
PlanMode plans.Mode
AutoApprove bool
Targets []addrs.Targetable
ForceReplace []addrs.AbsResourceInstance
Variables map[string]UnparsedVariableValue
// Some operations use root module variables only opportunistically or
// don't need them at all. If this flag is set, the backend must treat
// all variables as optional and provide an unknown value for any required
// variables that aren't set in order to allow partial evaluation against
// the resulting incomplete context.
//
// This flag is honored only if PlanFile isn't set. If PlanFile is set then
// the variables set in the plan are used instead, and they must be valid.
AllowUnsetVariables bool
// View implements the logic for all UI interactions.
View views.Operation
// Input/output/control options.
UIIn terraform.UIInput
UIOut terraform.UIOutput
// StateLocker is used to lock the state while providing UI feedback to the
// user. This will be replaced by the Backend to update the context.
//
// If state locking is not necessary, this should be set to a no-op
// implementation of clistate.Locker.
StateLocker clistate.Locker
// Workspace is the name of the workspace that this operation should run
// in, which controls which named state is used.
Workspace string
}
// HasConfig returns true if and only if the operation has a ConfigDir value
// that refers to a directory containing at least one Terraform configuration
// file.
func (o *Operation) HasConfig() bool {
return o.ConfigLoader.IsConfigDir(o.ConfigDir)
}
// Config loads the configuration that the operation applies to, using the
// ConfigDir and ConfigLoader fields within the receiving operation.
func (o *Operation) Config() (*configs.Config, tfdiags.Diagnostics) {
var diags tfdiags.Diagnostics
config, hclDiags := o.ConfigLoader.LoadConfig(o.ConfigDir)
diags = diags.Append(hclDiags)
return config, diags
}
// ReportResult is a helper for the common chore of setting the status of
// a running operation and showing any diagnostics produced during that
// operation.
//
// If the given diagnostics contains errors then the operation's result
// will be set to backend.OperationFailure. It will be set to
// backend.OperationSuccess otherwise. It will then use o.View.Diagnostics
// to show the given diagnostics before returning.
//
// Callers should feel free to do each of these operations separately in
// more complex cases where e.g. diagnostics are interleaved with other
// output, but terminating immediately after reporting error diagnostics is
// common and can be expressed concisely via this method.
func (o *Operation) ReportResult(op *RunningOperation, diags tfdiags.Diagnostics) {
if diags.HasErrors() {
op.Result = OperationFailure
} else {
op.Result = OperationSuccess
}
if o.View != nil {
o.View.Diagnostics(diags)
} else {
// Shouldn't generally happen, but if it does then we'll at least
// make some noise in the logs to help us spot it.
if len(diags) != 0 {
log.Printf(
"[ERROR] Backend needs to report diagnostics but View is not set:\n%s",
diags.ErrWithWarnings(),
)
}
}
}
// RunningOperation is the result of starting an operation.
type RunningOperation struct {
// For implementers of a backend, this context should not wrap the
// passed in context. Otherwise, cancelling 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
// Stop requests the operation to complete early, by calling Stop on all
// the plugins. If the process needs to terminate immediately, call Cancel.
Stop context.CancelFunc
// Cancel is the context.CancelFunc associated with the embedded context,
// and can be called to terminate the operation early.
// Once Cancel is called, the operation should return as soon as possible
// to avoid running operations during process exit.
Cancel context.CancelFunc
// Result is the exit status of the operation, populated only after the
// operation has completed.
Result OperationResult
// 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 *states.State
}
// OperationResult describes the result status of an operation.
type OperationResult int
const (
// OperationSuccess indicates that the operation completed as expected.
OperationSuccess OperationResult = 0
// OperationFailure indicates that the operation encountered some sort
// of error, and thus may have been only partially performed or not
// performed at all.
OperationFailure OperationResult = 1
)
func (r OperationResult) ExitStatus() int {
return int(r)
}
// If the argument is a path, Read loads it and returns the contents,
// otherwise the argument is assumed to be the desired contents and is simply
// returned.
func ReadPathOrContents(poc string) (string, error) {
if len(poc) == 0 {
return poc, nil
}
path := poc
if path[0] == '~' {
var err error
path, err = homedir.Expand(path)
if err != nil {
return path, err
}
}
if _, err := os.Stat(path); err == nil {
contents, err := ioutil.ReadFile(path)
if err != nil {
return string(contents), err
}
return string(contents), nil
}
return poc, nil
}