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|
package nodes
import (
"context"
"sync"
"time"
"gitlab.com/gitlab-org/gitaly/internal/praefect/metrics"
)
type nodeCandidate struct {
node Node
up bool
primary bool
statuses []bool
}
// localElector relies on an in-memory datastore to track the primary
// and secondaries. A single election strategy pertains to a single
// shard. It does NOT support multiple Praefect nodes or have any
// persistence. This is used mostly for testing and development.
type localElector struct {
m sync.RWMutex
failoverEnabled bool
shardName string
nodes []*nodeCandidate
primaryNode *nodeCandidate
}
// healthcheckThreshold is the number of consecutive healthpb.HealthCheckResponse_SERVING necessary
// for deeming a node "healthy"
const healthcheckThreshold = 3
func (n *nodeCandidate) isHealthy() bool {
if len(n.statuses) < healthcheckThreshold {
return false
}
for _, status := range n.statuses[len(n.statuses)-healthcheckThreshold:] {
if !status {
return false
}
}
return true
}
func newLocalElector(name string, failoverEnabled bool) *localElector {
return &localElector{
shardName: name,
failoverEnabled: failoverEnabled,
}
}
// addNode registers a primary or secondary in the internal
// datastore.
func (s *localElector) addNode(node Node, primary bool) {
localNode := nodeCandidate{
node: node,
primary: primary,
statuses: make([]bool, 0),
up: false,
}
// If failover hasn't been activated, we assume all nodes are up
// since health checks aren't run.
if !s.failoverEnabled {
localNode.up = true
}
s.m.Lock()
defer s.m.Unlock()
if primary {
s.primaryNode = &localNode
}
s.nodes = append(s.nodes, &localNode)
}
// Start launches a Goroutine to check the state of the nodes and
// continuously monitor their health via gRPC health checks.
func (s *localElector) start(bootstrapInterval, monitorInterval time.Duration) error {
s.bootstrap(bootstrapInterval)
go s.monitor(monitorInterval)
return nil
}
func (s *localElector) bootstrap(d time.Duration) {
timer := time.NewTimer(d)
defer timer.Stop()
for i := 0; i < healthcheckThreshold; i++ {
<-timer.C
ctx := context.TODO()
s.checkNodes(ctx)
timer.Reset(d)
}
}
func (s *localElector) monitor(d time.Duration) {
ticker := time.NewTicker(d)
defer ticker.Stop()
for {
ctx := context.Background()
s.checkNodes(ctx)
}
}
// checkNodes issues a gRPC health check for each node managed by the
// shard.
func (s *localElector) checkNodes(ctx context.Context) {
defer s.updateMetrics()
for _, n := range s.nodes {
status, _ := n.node.check(ctx)
n.statuses = append(n.statuses, status)
if len(n.statuses) > healthcheckThreshold {
n.statuses = n.statuses[1:]
}
up := n.isHealthy()
n.up = up
}
if s.primaryNode != nil && s.primaryNode.isHealthy() {
return
}
var newPrimary *nodeCandidate
for _, node := range s.nodes {
if !node.primary && node.isHealthy() {
newPrimary = node
break
}
}
if newPrimary == nil {
return
}
s.m.Lock()
defer s.m.Unlock()
s.primaryNode.primary = false
s.primaryNode = newPrimary
newPrimary.primary = true
}
// GetPrimary gets the primary of a shard. If no primary exists, it will
// be nil. If a primary has been elected but is down, err will be
// ErrPrimaryNotHealthy.
func (s *localElector) GetPrimary() (Node, error) {
s.m.RLock()
defer s.m.RUnlock()
if s.primaryNode == nil {
return nil, ErrPrimaryNotHealthy
}
if !s.primaryNode.up {
return s.primaryNode.node, ErrPrimaryNotHealthy
}
return s.primaryNode.node, nil
}
// GetSecondaries gets the secondaries of a shard
func (s *localElector) GetSecondaries() ([]Node, error) {
s.m.RLock()
defer s.m.RUnlock()
var secondaries []Node
for _, n := range s.nodes {
if !n.primary {
secondaries = append(secondaries, n.node)
}
}
return secondaries, nil
}
func (s *localElector) updateMetrics() {
s.m.RLock()
defer s.m.RUnlock()
for _, node := range s.nodes {
var val float64
if node.primary {
val = 1
}
metrics.PrimaryGauge.WithLabelValues(s.shardName, node.node.GetStorage()).Set(val)
}
}
|
