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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.List() {
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
destroyMap := make(map[string][]dag.Vertex)
for _, v := range g.Vertices() {
dn, ok := v.(GraphNodeDestroyerCBD)
if !ok {
continue
}
dern, ok := v.(GraphNodeDestroyer)
if !ok {
continue
}
if !dn.CreateBeforeDestroy() {
continue
}
// Find the destroy edge. There should only be one.
for _, e := range g.EdgesTo(v) {
// Not a destroy edge, ignore it
de, ok := e.(*DestroyEdge)
if !ok {
continue
}
log.Printf("[TRACE] CBDEdgeTransformer: inverting edge: %s => %s",
dag.VertexName(de.Source()), dag.VertexName(de.Target()))
// Found it! Invert.
g.RemoveEdge(de)
applyNode := de.Source()
destroyNode := de.Target()
g.Connect(&DestroyEdge{S: destroyNode, T: applyNode})
}
// If the address has an index, we strip that. Our depMap creation
// graph doesn't expand counts so we don't currently get _exact_
// dependencies. One day when we limit dependencies more exactly
// this will have to change. We have a test case covering this
// (depNonCBDCountBoth) so it'll be caught.
addr := dern.DestroyAddr()
key := addr.ContainingResource().String()
// Add this to the list of nodes that we need to fix up
// the edges for (step 2 above in the docs).
destroyMap[key] = append(destroyMap[key], v)
}
// If we have no CBD nodes, then our work here is done
if len(destroyMap) == 0 {
return nil
}
// We have CBD nodes. We now have to move on to the much more difficult
// task of connecting dependencies of the creation side of the destroy
// to the destruction node. The easiest way to explain this is an example:
//
// Given a pre-destroy dependence of: A => B
// And A has CBD set.
//
// The resulting graph should be: A => B => A_d
//
// They key here is that B happens before A is destroyed. This is to
// facilitate the primary purpose for CBD: making sure that downstreams
// are properly updated to avoid downtime before the resource is destroyed.
//
// We can't trust that the resource being destroyed or anything that
// depends on it is actually in our current graph so we make a new
// graph in order to determine those dependencies and add them in.
log.Printf("[TRACE] CBDEdgeTransformer: building graph to find dependencies...")
depMap, err := t.depMap(destroyMap)
if err != nil {
return err
}
// We now have the mapping of resource addresses to the destroy
// nodes they need to depend on. We now go through our own vertices to
// find any matching these addresses and make the connection.
for _, v := range g.Vertices() {
// We're looking for creators
rn, ok := v.(GraphNodeCreator)
if !ok {
continue
}
// Get the address
addr := rn.CreateAddr()
// If the address has an index, we strip that. Our depMap creation
// graph doesn't expand counts so we don't currently get _exact_
// dependencies. One day when we limit dependencies more exactly
// this will have to change. We have a test case covering this
// (depNonCBDCount) so it'll be caught.
key := addr.ContainingResource().String()
// If there is nothing this resource should depend on, ignore it
dns, ok := depMap[key]
if !ok {
continue
}
// We have nodes! Make the connection
for _, dn := range dns {
log.Printf("[TRACE] CBDEdgeTransformer: destroy depends on dependence: %s => %s",
dag.VertexName(dn), dag.VertexName(v))
g.Connect(dag.BasicEdge(dn, v))
}
}
return nil
}
func (t *CBDEdgeTransformer) depMap(destroyMap map[string][]dag.Vertex) (map[string][]dag.Vertex, error) {
// Build the graph of our config, this ensures that all resources
// are present in the graph.
g, diags := (&BasicGraphBuilder{
Steps: []GraphTransformer{
&FlatConfigTransformer{Config: t.Config},
&AttachResourceConfigTransformer{Config: t.Config},
&AttachStateTransformer{State: t.State},
&AttachSchemaTransformer{Schemas: t.Schemas},
&ReferenceTransformer{},
},
Name: "CBDEdgeTransformer",
}).Build(nil)
if diags.HasErrors() {
return nil, diags.Err()
}
// Using this graph, build the list of destroy nodes that each resource
// address should depend on. For example, when we find B, we map the
// address of B to A_d in the "depMap" variable below.
depMap := make(map[string][]dag.Vertex)
for _, v := range g.Vertices() {
// We're looking for resources.
rn, ok := v.(GraphNodeResource)
if !ok {
continue
}
// Get the address
addr := rn.ResourceAddr()
key := addr.String()
// Get the destroy nodes that are destroying this resource.
// If there aren't any, then we don't need to worry about
// any connections.
dns, ok := destroyMap[key]
if !ok {
continue
}
// Get the nodes that depend on this on. In the example above:
// finding B in A => B.
for _, v := range g.UpEdges(v).List() {
// We're looking for resources.
rn, ok := v.(GraphNodeResource)
if !ok {
continue
}
// Keep track of the destroy nodes that this address
// needs to depend on.
key := rn.ResourceAddr().String()
depMap[key] = append(depMap[key], dns...)
}
}
return depMap, nil
}
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