aboutsummaryrefslogtreecommitdiff
path: root/libpod/container_graph.go
blob: da93be77dff0ea43047e644cf4240df40663b7b7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
package libpod

import (
	"context"
	"strings"

	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
)

type containerNode struct {
	id         string
	container  *Container
	dependsOn  []*containerNode
	dependedOn []*containerNode
}

type containerGraph struct {
	nodes              map[string]*containerNode
	noDepNodes         []*containerNode
	notDependedOnNodes map[string]*containerNode
}

func buildContainerGraph(ctrs []*Container) (*containerGraph, error) {
	graph := new(containerGraph)
	graph.nodes = make(map[string]*containerNode)
	graph.notDependedOnNodes = make(map[string]*containerNode)

	// Start by building all nodes, with no edges
	for _, ctr := range ctrs {
		ctrNode := new(containerNode)
		ctrNode.id = ctr.ID()
		ctrNode.container = ctr

		graph.nodes[ctr.ID()] = ctrNode
		graph.notDependedOnNodes[ctr.ID()] = ctrNode
	}

	// Now add edges based on dependencies
	for _, node := range graph.nodes {
		deps := node.container.Dependencies()
		for _, dep := range deps {
			// Get the dep's node
			depNode, ok := graph.nodes[dep]
			if !ok {
				return nil, errors.Wrapf(ErrNoSuchCtr, "container %s depends on container %s not found in input list", node.id, dep)
			}

			// Add the dependent node to the node's dependencies
			// And add the node to the dependent node's dependedOn
			node.dependsOn = append(node.dependsOn, depNode)
			depNode.dependedOn = append(depNode.dependedOn, node)

			// The dependency now has something depending on it
			delete(graph.notDependedOnNodes, dep)
		}

		// Maintain a list of nodes with no dependencies
		// (no edges coming from them)
		if len(deps) == 0 {
			graph.noDepNodes = append(graph.noDepNodes, node)
		}
	}

	// Need to do cycle detection
	// We cannot start or stop if there are cyclic dependencies
	cycle, err := detectCycles(graph)
	if err != nil {
		return nil, err
	} else if cycle {
		return nil, errors.Wrapf(ErrInternal, "cycle found in container dependency graph")
	}

	return graph, nil
}

// Detect cycles in a container graph using Tarjan's strongly connected
// components algorithm
// Return true if a cycle is found, false otherwise
func detectCycles(graph *containerGraph) (bool, error) {
	type nodeInfo struct {
		index   int
		lowLink int
		onStack bool
	}

	index := 0

	nodes := make(map[string]*nodeInfo)
	stack := make([]*containerNode, 0, len(graph.nodes))

	var strongConnect func(*containerNode) (bool, error)
	strongConnect = func(node *containerNode) (bool, error) {
		logrus.Debugf("Strongconnecting node %s", node.id)

		info := new(nodeInfo)
		info.index = index
		info.lowLink = index
		index = index + 1

		nodes[node.id] = info

		stack = append(stack, node)

		info.onStack = true

		logrus.Debugf("Pushed %s onto stack", node.id)

		// Work through all nodes we point to
		for _, successor := range node.dependsOn {
			if _, ok := nodes[successor.id]; !ok {
				logrus.Debugf("Recursing to successor node %s", successor.id)

				cycle, err := strongConnect(successor)
				if err != nil {
					return false, err
				} else if cycle {
					return true, nil
				}

				successorInfo := nodes[successor.id]
				if successorInfo.lowLink < info.lowLink {
					info.lowLink = successorInfo.lowLink
				}
			} else {
				successorInfo := nodes[successor.id]
				if successorInfo.index < info.lowLink && successorInfo.onStack {
					info.lowLink = successorInfo.index
				}
			}
		}

		if info.lowLink == info.index {
			l := len(stack)
			if l == 0 {
				return false, errors.Wrapf(ErrInternal, "empty stack in detectCycles")
			}

			// Pop off the stack
			topOfStack := stack[l-1]
			stack = stack[:l-1]

			// Popped item is no longer on the stack, mark as such
			topInfo, ok := nodes[topOfStack.id]
			if !ok {
				return false, errors.Wrapf(ErrInternal, "error finding node info for %s", topOfStack.id)
			}
			topInfo.onStack = false

			logrus.Debugf("Finishing node %s. Popped %s off stack", node.id, topOfStack.id)

			// If the top of the stack is not us, we have found a
			// cycle
			if topOfStack.id != node.id {
				return true, nil
			}
		}

		return false, nil
	}

	for id, node := range graph.nodes {
		if _, ok := nodes[id]; !ok {
			cycle, err := strongConnect(node)
			if err != nil {
				return false, err
			} else if cycle {
				return true, nil
			}
		}
	}

	return false, nil
}

// Visit a node on a container graph and start the container, or set an error if
// a dependency failed to start. if restart is true, startNode will restart the node instead of starting it.
func startNode(ctx context.Context, node *containerNode, setError bool, ctrErrors map[string]error, ctrsVisited map[string]bool, restart bool) {
	// First, check if we have already visited the node
	if ctrsVisited[node.id] {
		return
	}

	// If setError is true, a dependency of us failed
	// Mark us as failed and recurse
	if setError {
		// Mark us as visited, and set an error
		ctrsVisited[node.id] = true
		ctrErrors[node.id] = errors.Wrapf(ErrCtrStateInvalid, "a dependency of container %s failed to start", node.id)

		// Hit anyone who depends on us, and set errors on them too
		for _, successor := range node.dependedOn {
			startNode(ctx, successor, true, ctrErrors, ctrsVisited, restart)
		}

		return
	}

	// Have all our dependencies started?
	// If not, don't visit the node yet
	depsVisited := true
	for _, dep := range node.dependsOn {
		depsVisited = depsVisited && ctrsVisited[dep.id]
	}
	if !depsVisited {
		// Don't visit us yet, all dependencies are not up
		// We'll hit the dependencies eventually, and when we do it will
		// recurse here
		return
	}

	// Going to try to start the container, mark us as visited
	ctrsVisited[node.id] = true

	ctrErrored := false

	// Check if dependencies are running
	// Graph traversal means we should have started them
	// But they could have died before we got here
	// Does not require that the container be locked, we only need to lock
	// the dependencies
	depsStopped, err := node.container.checkDependenciesRunning()
	if err != nil {
		ctrErrors[node.id] = err
		ctrErrored = true
	} else if len(depsStopped) > 0 {
		// Our dependencies are not running
		depsList := strings.Join(depsStopped, ",")
		ctrErrors[node.id] = errors.Wrapf(ErrCtrStateInvalid, "the following dependencies of container %s are not running: %s", node.id, depsList)
		ctrErrored = true
	}

	// Lock before we start
	node.container.lock.Lock()

	// Sync the container to pick up current state
	if !ctrErrored {
		if err := node.container.syncContainer(); err != nil {
			ctrErrored = true
			ctrErrors[node.id] = err
		}
	}

	// Start the container (only if it is not running)
	if !ctrErrored {
		if !restart && node.container.state.State != ContainerStateRunning {
			if err := node.container.initAndStart(ctx); err != nil {
				ctrErrored = true
				ctrErrors[node.id] = err
			}
		}
		if restart && node.container.state.State != ContainerStatePaused && node.container.state.State != ContainerStateUnknown {
			if err := node.container.restartWithTimeout(ctx, node.container.config.StopTimeout); err != nil {
				ctrErrored = true
				ctrErrors[node.id] = err
			}
		}
	}

	node.container.lock.Unlock()

	// Recurse to anyone who depends on us and start them
	for _, successor := range node.dependedOn {
		startNode(ctx, successor, ctrErrored, ctrErrors, ctrsVisited, restart)
	}

	return
}