vendor/github.com/hashicorp/terraform/terraform/transform_destroy_edge.go

   1 package terraform
   2
   3 import (
   4         "log"
   5
   6         "github.com/hashicorp/terraform/config/module"
   7         "github.com/hashicorp/terraform/dag"
   8 )
   9
  10 // GraphNodeDestroyer must be implemented by nodes that destroy resources.
  11 type GraphNodeDestroyer interface {
  12         dag.Vertex
  13
  14         // ResourceAddr is the address of the resource that is being
  15         // destroyed by this node. If this returns nil, then this node
  16         // is not destroying anything.
  17         DestroyAddr() *ResourceAddress
  18 }
  19
  20 // GraphNodeCreator must be implemented by nodes that create OR update resources.
  21 type GraphNodeCreator interface {
  22         // ResourceAddr is the address of the resource being created or updated
  23         CreateAddr() *ResourceAddress
  24 }
  25
  26 // DestroyEdgeTransformer is a GraphTransformer that creates the proper
  27 // references for destroy resources. Destroy resources are more complex
  28 // in that they must be depend on the destruction of resources that
  29 // in turn depend on the CREATION of the node being destroy.
  30 //
  31 // That is complicated. Visually:
  32 //
  33 //   B_d -> A_d -> A -> B
  34 //
  35 // Notice that A destroy depends on B destroy, while B create depends on
  36 // A create. They're inverted. This must be done for example because often
  37 // dependent resources will block parent resources from deleting. Concrete
  38 // example: VPC with subnets, the VPC can't be deleted while there are
  39 // still subnets.
  40 type DestroyEdgeTransformer struct {
  41         // These are needed to properly build the graph of dependencies
  42         // to determine what a destroy node depends on. Any of these can be nil.
  43         Module *module.Tree
  44         State  *State
  45 }
  46
  47 func (t *DestroyEdgeTransformer) Transform(g *Graph) error {
  48         log.Printf("[TRACE] DestroyEdgeTransformer: Beginning destroy edge transformation...")
  49
  50         // Build a map of what is being destroyed (by address string) to
  51         // the list of destroyers. In general there will only be one destroyer
  52         // but to make it more robust we support multiple.
  53         destroyers := make(map[string][]GraphNodeDestroyer)
  54         for _, v := range g.Vertices() {
  55                 dn, ok := v.(GraphNodeDestroyer)
  56                 if !ok {
  57                         continue
  58                 }
  59
  60                 addr := dn.DestroyAddr()
  61                 if addr == nil {
  62                         continue
  63                 }
  64
  65                 key := addr.String()
  66                 log.Printf(
  67                         "[TRACE] DestroyEdgeTransformer: %s destroying %q",
  68                         dag.VertexName(dn), key)
  69                 destroyers[key] = append(destroyers[key], dn)
  70         }
  71
  72         // If we aren't destroying anything, there will be no edges to make
  73         // so just exit early and avoid future work.
  74         if len(destroyers) == 0 {
  75                 return nil
  76         }
  77
  78         // Go through and connect creators to destroyers. Going along with
  79         // our example, this makes: A_d => A
  80         for _, v := range g.Vertices() {
  81                 cn, ok := v.(GraphNodeCreator)
  82                 if !ok {
  83                         continue
  84                 }
  85
  86                 addr := cn.CreateAddr()
  87                 if addr == nil {
  88                         continue
  89                 }
  90
  91                 key := addr.String()
  92                 ds := destroyers[key]
  93                 if len(ds) == 0 {
  94                         continue
  95                 }
  96
  97                 for _, d := range ds {
  98                         // For illustrating our example
  99                         a_d := d.(dag.Vertex)
 100                         a := v
 101
 102                         log.Printf(
 103                                 "[TRACE] DestroyEdgeTransformer: connecting creator/destroyer: %s, %s",
 104                                 dag.VertexName(a), dag.VertexName(a_d))
 105
 106                         g.Connect(&DestroyEdge{S: a, T: a_d})
 107                 }
 108         }
 109
 110         // This is strange but is the easiest way to get the dependencies
 111         // of a node that is being destroyed. We use another graph to make sure
 112         // the resource is in the graph and ask for references. We have to do this
 113         // because the node that is being destroyed may NOT be in the graph.
 114         //
 115         // Example: resource A is force new, then destroy A AND create A are
 116         // in the graph. BUT if resource A is just pure destroy, then only
 117         // destroy A is in the graph, and create A is not.
 118         providerFn := func(a *NodeAbstractProvider) dag.Vertex {
 119                 return &NodeApplyableProvider{NodeAbstractProvider: a}
 120         }
 121         steps := []GraphTransformer{
 122                 // Add the local values
 123                 &LocalTransformer{Module: t.Module},
 124
 125                 // Add outputs and metadata
 126                 &OutputTransformer{Module: t.Module},
 127                 &AttachResourceConfigTransformer{Module: t.Module},
 128                 &AttachStateTransformer{State: t.State},
 129
 130                 TransformProviders(nil, providerFn, t.Module),
 131
 132                 // Add all the variables. We can depend on resources through
 133                 // variables due to module parameters, and we need to properly
 134                 // determine that.
 135                 &RootVariableTransformer{Module: t.Module},
 136                 &ModuleVariableTransformer{Module: t.Module},
 137
 138                 &ReferenceTransformer{},
 139         }
 140
 141         // Go through all the nodes being destroyed and create a graph.
 142         // The resulting graph is only of things being CREATED. For example,
 143         // following our example, the resulting graph would be:
 144         //
 145         //   A, B (with no edges)
 146         //
 147         var tempG Graph
 148         var tempDestroyed []dag.Vertex
 149         for d, _ := range destroyers {
 150                 // d is what is being destroyed. We parse the resource address
 151                 // which it came from it is a panic if this fails.
 152                 addr, err := ParseResourceAddress(d)
 153                 if err != nil {
 154                         panic(err)
 155                 }
 156
 157                 // This part is a little bit weird but is the best way to
 158                 // find the dependencies we need to: build a graph and use the
 159                 // attach config and state transformers then ask for references.
 160                 abstract := &NodeAbstractResource{Addr: addr}
 161                 tempG.Add(abstract)
 162                 tempDestroyed = append(tempDestroyed, abstract)
 163
 164                 // We also add the destroy version here since the destroy can
 165                 // depend on things that the creation doesn't (destroy provisioners).
 166                 destroy := &NodeDestroyResource{NodeAbstractResource: abstract}
 167                 tempG.Add(destroy)
 168                 tempDestroyed = append(tempDestroyed, destroy)
 169         }
 170
 171         // Run the graph transforms so we have the information we need to
 172         // build references.
 173         for _, s := range steps {
 174                 if err := s.Transform(&tempG); err != nil {
 175                         return err
 176                 }
 177         }
 178
 179         log.Printf("[TRACE] DestroyEdgeTransformer: reference graph: %s", tempG.String())
 180
 181         // Go through all the nodes in the graph and determine what they
 182         // depend on.
 183         for _, v := range tempDestroyed {
 184                 // Find all ancestors of this to determine the edges we'll depend on
 185                 vs, err := tempG.Ancestors(v)
 186                 if err != nil {
 187                         return err
 188                 }
 189
 190                 refs := make([]dag.Vertex, 0, vs.Len())
 191                 for _, raw := range vs.List() {
 192                         refs = append(refs, raw.(dag.Vertex))
 193                 }
 194
 195                 refNames := make([]string, len(refs))
 196                 for i, ref := range refs {
 197                         refNames[i] = dag.VertexName(ref)
 198                 }
 199                 log.Printf(
 200                         "[TRACE] DestroyEdgeTransformer: creation node %q references %s",
 201                         dag.VertexName(v), refNames)
 202
 203                 // If we have no references, then we won't need to do anything
 204                 if len(refs) == 0 {
 205                         continue
 206                 }
 207
 208                 // Get the destroy node for this. In the example of our struct,
 209                 // we are currently at B and we're looking for B_d.
 210                 rn, ok := v.(GraphNodeResource)
 211                 if !ok {
 212                         continue
 213                 }
 214
 215                 addr := rn.ResourceAddr()
 216                 if addr == nil {
 217                         continue
 218                 }
 219
 220                 dns := destroyers[addr.String()]
 221
 222                 // We have dependencies, check if any are being destroyed
 223                 // to build the list of things that we must depend on!
 224                 //
 225                 // In the example of the struct, if we have:
 226                 //
 227                 //   B_d => A_d => A => B
 228                 //
 229                 // Then at this point in the algorithm we started with B_d,
 230                 // we built B (to get dependencies), and we found A. We're now looking
 231                 // to see if A_d exists.
 232                 var depDestroyers []dag.Vertex
 233                 for _, v := range refs {
 234                         rn, ok := v.(GraphNodeResource)
 235                         if !ok {
 236                                 continue
 237                         }
 238
 239                         addr := rn.ResourceAddr()
 240                         if addr == nil {
 241                                 continue
 242                         }
 243
 244                         key := addr.String()
 245                         if ds, ok := destroyers[key]; ok {
 246                                 for _, d := range ds {
 247                                         depDestroyers = append(depDestroyers, d.(dag.Vertex))
 248                                         log.Printf(
 249                                                 "[TRACE] DestroyEdgeTransformer: destruction of %q depends on %s",
 250                                                 key, dag.VertexName(d))
 251                                 }
 252                         }
 253                 }
 254
 255                 // Go through and make the connections. Use the variable
 256                 // names "a_d" and "b_d" to reference our example.
 257                 for _, a_d := range dns {
 258                         for _, b_d := range depDestroyers {
 259                                 if b_d != a_d {
 260                                         g.Connect(dag.BasicEdge(b_d, a_d))
 261                                 }
 262                         }
 263                 }
 264         }
 265
 266         return nil
 267 }