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aggregator.go
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aggregator.go
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package watt
import (
"encoding/json"
"os/exec"
"strings"
"sync"
"time"
"github.com/datawire/ambassador/pkg/consulwatch"
"github.com/datawire/ambassador/pkg/limiter"
"github.com/datawire/ambassador/pkg/watt"
"github.com/datawire/ambassador/pkg/k8s"
"github.com/datawire/ambassador/pkg/supervisor"
)
type WatchHook func(p *supervisor.Process, snapshot string) WatchSet
type aggregator struct {
// Input channel used to tell us about kubernetes state.
KubernetesEvents chan k8sEvent
// Input channel used to tell us about consul endpoints.
ConsulEvents chan consulEvent
// Output channel used to communicate with the k8s watch manager.
k8sWatches chan<- []KubernetesWatchSpec
// Output channel used to communicate with the consul watch manager.
consulWatches chan<- []ConsulWatchSpec
// Output channel used to communicate with the invoker.
snapshots chan<- string
// We won't consider ourselves "bootstrapped" until we hear
// about all these kinds.
requiredKinds []string
watchHook WatchHook
limiter limiter.Limiter
ids map[string]bool
kubernetesResources map[string]map[string][]k8s.Resource
consulEndpoints map[string]consulwatch.Endpoints
bootstrapped bool
notifyMux sync.Mutex
errors map[string][]watt.Error
}
func NewAggregator(snapshots chan<- string, k8sWatches chan<- []KubernetesWatchSpec, consulWatches chan<- []ConsulWatchSpec,
requiredKinds []string, watchHook WatchHook, limiter limiter.Limiter) *aggregator {
return &aggregator{
KubernetesEvents: make(chan k8sEvent),
ConsulEvents: make(chan consulEvent),
k8sWatches: k8sWatches,
consulWatches: consulWatches,
snapshots: snapshots,
requiredKinds: requiredKinds,
watchHook: watchHook,
limiter: limiter,
ids: make(map[string]bool),
kubernetesResources: make(map[string]map[string][]k8s.Resource),
consulEndpoints: make(map[string]consulwatch.Endpoints),
errors: make(map[string][]watt.Error),
}
}
func (a *aggregator) Work(p *supervisor.Process) error {
// In order to invoke `maybeNotify`, which is a very time consuming
// operation, we coalesce events:
//
// 1. Be continuously reading all available events from
// a.KubernetesEvents and a.ConsulEvents and store k8sEvents
// in the potentialKubernetesEventSignal variable. This means
// at any given point (modulo caveats below), the
// potentialKubernetesEventSignal variable will have the
// latest Kubernetes event available.
//
// 2. At the same time, whenever there is capacity to write
// down the kubernetesEventProcessor channel, we send
// potentialKubernetesEventSignal to be processed.
//
// The anonymous goroutine below will be constantly reading
// from the kubernetesEventProcessor channel and performing
// a blocking a.maybeNotify(). This means that we can only
// *write* to the kubernetesEventProcessor channel when we are
// not currently processing an event, but when that happens, we
// will still read from a.KubernetesEvents and a.ConsulEvents
// and update potentialKubernetesEventSignal.
//
// There are three caveats to the above:
//
// 1. At startup, we don't yet have a event to write, but
// we're not processing anything, so we will try to write
// something down the kubernetesEventProcessor channel.
// To cope with this, the invoking goroutine will ignore events
// signals that have a event.skip flag.
//
// 2. If we process an event quickly, or if there aren't new
// events available, then we end up busy looping and
// sending the same potentialKubernetesEventSignal value down
// the kubernetesEventProcessor channel multiple times. To cope
// with this, whenever we have successfully written to the
// kubernetesEventProcessor channel, we do a *blocking* read of
// the next event from a.KubernetesEvents and a.ConsulEvents.
//
// 3. Always be calling a.setKubernetesResources as soon as we
// receive an event. This is a fast non-blocking call that
// update watches, we can't coalesce this call.
p.Ready()
type eventSignal struct {
kubernetesEvent k8sEvent
skip bool
}
kubernetesEventProcessor := make(chan eventSignal)
go func() {
for event := range kubernetesEventProcessor {
if event.skip {
// ignore the initial eventSignal to deal with the
// corner case where we haven't yet received an event yet.
continue
}
a.maybeNotify(p)
}
}()
potentialKubernetesEventSignal := eventSignal{kubernetesEvent: k8sEvent{}, skip: true}
for {
select {
case potentialKubernetesEvent := <-a.KubernetesEvents:
// if a new KubernetesEvents is available to be read,
// and we can't write to the kubernetesEventProcessor channel,
// then we will overwrite potentialKubernetesEvent
// with a newer event while still processing a.setKubernetesResources
a.setKubernetesResources(potentialKubernetesEvent)
potentialKubernetesEventSignal = eventSignal{kubernetesEvent: potentialKubernetesEvent, skip: false}
case kubernetesEventProcessor <- potentialKubernetesEventSignal:
// if we aren't currently blocked in
// a.maybeNotify() then the above goroutine will be
// reading from the kubernetesEventProcessor channel and we
// will send the current potentialKubernetesEventSignal
// value over the kubernetesEventProcessor channel to be
// processed
select {
case potentialKubernetesEvent := <-a.KubernetesEvents:
// here we do blocking read of the next event for caveat #2.
a.setKubernetesResources(potentialKubernetesEvent)
potentialKubernetesEventSignal = eventSignal{kubernetesEvent: potentialKubernetesEvent, skip: false}
case event := <-a.ConsulEvents:
a.updateConsulResources(event)
a.maybeNotify(p)
case <-p.Shutdown():
return nil
}
case event := <-a.ConsulEvents:
// we are always reading and processing ConsulEvents directly,
// not coalescing them.
a.updateConsulResources(event)
a.maybeNotify(p)
case <-p.Shutdown():
return nil
}
}
}
func (a *aggregator) updateConsulResources(event consulEvent) {
a.ids[event.WatchId] = true
a.consulEndpoints[event.Endpoints.Service] = event.Endpoints
}
func (a *aggregator) setKubernetesResources(event k8sEvent) {
if len(event.errors) > 0 {
for _, kError := range event.errors {
a.errors[kError.Source] = append(a.errors[kError.Source], kError)
}
return
}
a.ids[event.watchId] = true
submap, ok := a.kubernetesResources[event.watchId]
if !ok {
submap = make(map[string][]k8s.Resource)
a.kubernetesResources[event.watchId] = submap
}
submap[event.kind] = event.resources
}
func (a *aggregator) generateSnapshot() (string, error) {
k8sResources := make(map[string][]k8s.Resource)
for _, submap := range a.kubernetesResources {
for k, v := range submap {
k8sResources[k] = append(k8sResources[k], v...)
}
}
s := watt.Snapshot{
Consul: watt.ConsulSnapshot{Endpoints: a.consulEndpoints},
Kubernetes: k8sResources,
Errors: a.errors,
}
jsonBytes, err := json.MarshalIndent(s, "", " ")
if err != nil {
return "{}", err
}
return string(jsonBytes), nil
}
func (a *aggregator) isKubernetesBootstrapped(p *supervisor.Process) bool {
submap, sok := a.kubernetesResources[""]
if !sok {
return false
}
for _, k := range a.requiredKinds {
_, ok := submap[k]
if !ok {
return false
}
}
return true
}
// Returns true if the current state of the world is complete. The
// kubernetes state of the world is always complete by definition
// because the kubernetes client provides that guarantee. The
// aggregate state of the world is complete when any consul services
// referenced by kubernetes have populated endpoint information (even
// if the value of the populated info is an empty set of endpoints).
func (a *aggregator) isComplete(p *supervisor.Process, watchset WatchSet) bool {
complete := true
for _, w := range watchset.KubernetesWatches {
if _, ok := a.ids[w.WatchId()]; ok {
p.Debugf("initialized k8s watch: %s", w.WatchId())
} else {
complete = false
p.Debugf("waiting for k8s watch: %s", w.WatchId())
}
}
for _, w := range watchset.ConsulWatches {
if _, ok := a.ids[w.WatchId()]; ok {
p.Debugf("initialized consul watch: %s", w.WatchId())
} else {
complete = false
p.Debugf("waiting for consul watch: %s", w.WatchId())
}
}
return complete
}
func (a *aggregator) maybeNotify(p *supervisor.Process) {
now := time.Now()
delay := a.limiter.Limit(now)
if delay == 0 {
a.notify(p)
} else if delay > 0 {
time.AfterFunc(delay, func() {
a.notify(p)
})
}
}
func (a *aggregator) notify(p *supervisor.Process) {
a.notifyMux.Lock()
defer a.notifyMux.Unlock()
if !a.isKubernetesBootstrapped(p) {
return
}
watchset := a.getWatches(p)
p.Debugf("found %d kubernetes watches", len(watchset.KubernetesWatches))
p.Debugf("found %d consul watches", len(watchset.ConsulWatches))
a.k8sWatches <- watchset.KubernetesWatches
a.consulWatches <- watchset.ConsulWatches
if !a.bootstrapped && a.isComplete(p, watchset) {
p.Logf("bootstrapped!")
a.bootstrapped = true
}
if a.bootstrapped {
snapshot, err := a.generateSnapshot()
if err != nil {
p.Logf("generate snapshot failed %v", err)
return
}
a.snapshots <- snapshot
}
}
func (a *aggregator) getWatches(p *supervisor.Process) WatchSet {
snapshot, err := a.generateSnapshot()
if err != nil {
p.Logf("generate snapshot failed %v", err)
return WatchSet{}
}
result := a.watchHook(p, snapshot)
return result.interpolate()
}
func ExecWatchHook(watchHooks []string) WatchHook {
return func(p *supervisor.Process, snapshot string) WatchSet {
result := WatchSet{}
for _, hook := range watchHooks {
ws := invokeHook(p, hook, snapshot)
result.KubernetesWatches = append(result.KubernetesWatches, ws.KubernetesWatches...)
result.ConsulWatches = append(result.ConsulWatches, ws.ConsulWatches...)
}
return result
}
}
func lines(st string) []string {
return strings.Split(st, "\n")
}
func invokeHook(p *supervisor.Process, hook, snapshot string) WatchSet {
cmd := exec.Command("sh", "-c", hook)
cmd.Stdin = strings.NewReader(snapshot)
var watches, errors strings.Builder
cmd.Stdout = &watches
cmd.Stderr = &errors
err := cmd.Run()
stderr := errors.String()
if stderr != "" {
for _, line := range lines(stderr) {
p.Logf("watch hook stderr: %s", line)
}
}
if err != nil {
p.Logf("watch hook failed: %v", err)
return WatchSet{}
}
encoded := watches.String()
decoder := json.NewDecoder(strings.NewReader(encoded))
decoder.DisallowUnknownFields()
result := WatchSet{}
err = decoder.Decode(&result)
if err != nil {
for _, line := range lines(encoded) {
p.Debugf("watch hook: %s", line)
}
p.Logf("watchset decode failed: %v", err)
return WatchSet{}
}
return result
}