terraform/terraform/transform_destroy_cbd.go

170 lines
5.7 KiB
Go

package terraform
import (
"fmt"
"log"
"github.com/hashicorp/terraform/configs"
"github.com/hashicorp/terraform/dag"
"github.com/hashicorp/terraform/states"
)
// GraphNodeDestroyerCBD must be implemented by nodes that might be
// create-before-destroy destroyers, or might plan a create-before-destroy
// action.
type GraphNodeDestroyerCBD interface {
// CreateBeforeDestroy returns true if this node represents a node
// that is doing a CBD.
CreateBeforeDestroy() bool
// ModifyCreateBeforeDestroy is called when the CBD state of a node
// is changed dynamically. This can return an error if this isn't
// allowed.
ModifyCreateBeforeDestroy(bool) error
}
// GraphNodeAttachDestroyer is implemented by applyable nodes that have a
// companion destroy node. This allows the creation node to look up the status
// of the destroy node and determine if it needs to depose the existing state,
// or replace it.
// If a node is not marked as create-before-destroy in the configuration, but a
// dependency forces that status, only the destroy node will be aware of that
// status.
type GraphNodeAttachDestroyer interface {
// AttachDestroyNode takes a destroy node and saves a reference to that
// node in the receiver, so it can later check the status of
// CreateBeforeDestroy().
AttachDestroyNode(n GraphNodeDestroyerCBD)
}
// ForcedCBDTransformer detects when a particular CBD-able graph node has
// dependencies with another that has create_before_destroy set that require
// it to be forced on, and forces it on.
//
// This must be used in the plan graph builder to ensure that
// create_before_destroy settings are properly propagated before constructing
// the planned changes. This requires that the plannable resource nodes
// implement GraphNodeDestroyerCBD.
type ForcedCBDTransformer struct {
}
func (t *ForcedCBDTransformer) Transform(g *Graph) error {
for _, v := range g.Vertices() {
dn, ok := v.(GraphNodeDestroyerCBD)
if !ok {
continue
}
if !dn.CreateBeforeDestroy() {
// If there are no CBD decendent (dependent nodes), then we
// do nothing here.
if !t.hasCBDDescendent(g, v) {
log.Printf("[TRACE] ForcedCBDTransformer: %q (%T) has no CBD descendent, so skipping", dag.VertexName(v), v)
continue
}
// If this isn't naturally a CBD node, this means that an descendent is
// and we need to auto-upgrade this node to CBD. We do this because
// a CBD node depending on non-CBD will result in cycles. To avoid this,
// we always attempt to upgrade it.
log.Printf("[TRACE] ForcedCBDTransformer: forcing create_before_destroy on for %q (%T)", dag.VertexName(v), v)
if err := dn.ModifyCreateBeforeDestroy(true); err != nil {
return fmt.Errorf(
"%s: must have create before destroy enabled because "+
"a dependent resource has CBD enabled. However, when "+
"attempting to automatically do this, an error occurred: %s",
dag.VertexName(v), err)
}
} else {
log.Printf("[TRACE] ForcedCBDTransformer: %q (%T) already has create_before_destroy set", dag.VertexName(v), v)
}
}
return nil
}
// hasCBDDescendent returns true if any descendent (node that depends on this)
// has CBD set.
func (t *ForcedCBDTransformer) hasCBDDescendent(g *Graph, v dag.Vertex) bool {
s, _ := g.Descendents(v)
if s == nil {
return true
}
for _, ov := range s {
dn, ok := ov.(GraphNodeDestroyerCBD)
if !ok {
continue
}
if dn.CreateBeforeDestroy() {
// some descendent is CreateBeforeDestroy, so we need to follow suit
log.Printf("[TRACE] ForcedCBDTransformer: %q has CBD descendent %q", dag.VertexName(v), dag.VertexName(ov))
return true
}
}
return false
}
// CBDEdgeTransformer modifies the edges of CBD nodes that went through
// the DestroyEdgeTransformer to have the right dependencies. There are
// two real tasks here:
//
// 1. With CBD, the destroy edge is inverted: the destroy depends on
// the creation.
//
// 2. A_d must depend on resources that depend on A. This is to enable
// the destroy to only happen once nodes that depend on A successfully
// update to A. Example: adding a web server updates the load balancer
// before deleting the old web server.
//
// This transformer requires that a previous transformer has already forced
// create_before_destroy on for nodes that are depended on by explicit CBD
// nodes. This is the logic in ForcedCBDTransformer, though in practice we
// will get here by recording the CBD-ness of each change in the plan during
// the plan walk and then forcing the nodes into the appropriate setting during
// DiffTransformer when building the apply graph.
type CBDEdgeTransformer struct {
// Module and State are only needed to look up dependencies in
// any way possible. Either can be nil if not availabile.
Config *configs.Config
State *states.State
// If configuration is present then Schemas is required in order to
// obtain schema information from providers and provisioners so we can
// properly resolve implicit dependencies.
Schemas *Schemas
}
func (t *CBDEdgeTransformer) Transform(g *Graph) error {
// Go through and reverse any destroy edges
for _, v := range g.Vertices() {
dn, ok := v.(GraphNodeDestroyerCBD)
if !ok {
continue
}
if _, ok = v.(GraphNodeDestroyer); !ok {
continue
}
if !dn.CreateBeforeDestroy() {
continue
}
// Find the resource edges
for _, e := range g.EdgesTo(v) {
src := e.Source()
// If source is a create node, invert the edge.
// This covers both the node's own creator, as well as reversing
// any dependants' edges.
if _, ok := src.(GraphNodeCreator); ok {
log.Printf("[TRACE] CBDEdgeTransformer: reversing edge %s -> %s", dag.VertexName(src), dag.VertexName(v))
g.RemoveEdge(e)
g.Connect(dag.BasicEdge(v, src))
}
}
}
return nil
}