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package nodes
import (
"context"
"sync"
"time"
"github.com/sirupsen/logrus"
"gitlab.com/gitlab-org/gitaly/internal/praefect/metrics"
)
// 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
shardName string
nodes []Node
primaryNode Node
log logrus.FieldLogger
doneCh chan struct{}
}
func newLocalElector(name string, log logrus.FieldLogger, ns []*nodeStatus) *localElector {
nodes := make([]Node, len(ns))
for i, n := range ns {
nodes[i] = n
}
return &localElector{
shardName: name,
log: log.WithField("virtual_storage", name),
nodes: nodes[:],
primaryNode: nodes[0],
doneCh: make(chan struct{}),
}
}
// 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) {
s.bootstrap(bootstrapInterval)
go s.monitor(monitorInterval)
}
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()
if err := s.checkNodes(ctx); err != nil {
s.log.WithError(err).Warn("error checking nodes")
}
timer.Reset(d)
}
}
func (s *localElector) monitor(d time.Duration) {
ticker := time.NewTicker(d)
defer ticker.Stop()
ctx := context.Background()
for {
select {
case <-s.doneCh:
return
case <-ticker.C:
}
err := s.checkNodes(ctx)
if err != nil {
s.log.WithError(err).Warn("error checking nodes")
}
}
}
func (s *localElector) stop() {
close(s.doneCh)
}
// checkNodes issues a gRPC health check for each node managed by the
// shard.
func (s *localElector) checkNodes(ctx context.Context) error {
defer s.updateMetrics()
var wg sync.WaitGroup
for _, n := range s.nodes {
wg.Add(1)
go func(n Node) {
defer wg.Done()
_, _ = n.CheckHealth(ctx)
}(n)
}
wg.Wait()
s.m.Lock()
defer s.m.Unlock()
if s.primaryNode.IsHealthy() {
return nil
}
var newPrimary Node
for _, node := range s.nodes {
if node != s.primaryNode && node.IsHealthy() {
newPrimary = node
break
}
}
if newPrimary == nil {
return ErrPrimaryNotHealthy
}
s.primaryNode = newPrimary
return nil
}
// GetShard gets the current status of the shard. If primary is not elected
// or it is unhealthy and failover is enabled, ErrPrimaryNotHealthy is
// returned.
func (s *localElector) GetShard(ctx context.Context) (Shard, error) {
s.m.RLock()
primary := s.primaryNode
s.m.RUnlock()
if primary == nil {
return Shard{}, ErrPrimaryNotHealthy
}
if !primary.IsHealthy() {
return Shard{}, ErrPrimaryNotHealthy
}
var secondaries []Node
for _, n := range s.nodes {
if n != primary {
secondaries = append(secondaries, n)
}
}
return Shard{
Primary: primary,
Secondaries: secondaries,
}, nil
}
func (s *localElector) updateMetrics() {
s.m.RLock()
primary := s.primaryNode
s.m.RUnlock()
for _, n := range s.nodes {
var val float64
if n == primary {
val = 1
}
metrics.PrimaryGauge.WithLabelValues(s.shardName, n.GetStorage()).Set(val)
}
}
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