open-consul/agent/checks/alias.go

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package checks
import (
"fmt"
"sync"
"time"
"github.com/hashicorp/consul/agent/structs"
"github.com/hashicorp/consul/api"
)
// Constants related to alias check backoff.
const (
checkAliasBackoffMin = 3 // 3 attempts before backing off
checkAliasBackoffMaxWait = 1 * time.Minute // maximum backoff wait time
)
// CheckAlias is a check type that aliases the health of another service
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// instance or node. If the service aliased has any critical health checks, then
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// this check is critical. If the service has no critical but warnings,
// then this check is warning, and if a service has only passing checks, then
// this check is passing.
type CheckAlias struct {
Node string // Node name of the service. If empty, assumed to be this node.
ServiceID structs.ServiceID // ID (not name) of the service to alias
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CheckID structs.CheckID // ID of this check
RPC RPC // Used to query remote server if necessary
RPCReq structs.NodeSpecificRequest // Base request
Notify AliasNotifier // For updating the check state
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stop bool
stopCh chan struct{}
stopLock sync.Mutex
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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stopWg sync.WaitGroup
structs.EnterpriseMeta
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}
// AliasNotifier is a CheckNotifier specifically for the Alias check.
// This requires additional methods that are satisfied by the agent
// local state.
type AliasNotifier interface {
CheckNotifier
AddAliasCheck(structs.CheckID, structs.ServiceID, chan<- struct{}) error
RemoveAliasCheck(structs.CheckID, structs.ServiceID)
Checks(*structs.EnterpriseMeta) map[structs.CheckID]*structs.HealthCheck
}
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// Start is used to start the check, runs until Stop() func (c *CheckAlias) Start() {
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func (c *CheckAlias) Start() {
c.stopLock.Lock()
defer c.stopLock.Unlock()
c.stop = false
c.stopCh = make(chan struct{})
go c.run(c.stopCh)
}
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// Stop is used to stop the check.
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func (c *CheckAlias) Stop() {
c.stopLock.Lock()
if !c.stop {
c.stop = true
close(c.stopCh)
}
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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c.stopLock.Unlock()
// Wait until the associated goroutine is definitely complete before
// returning to the caller. This is to prevent the new and old checks from
// both updating the state of the alias check using possibly stale
// information.
c.stopWg.Wait()
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}
// run is invoked in a goroutine until Stop() is called.
func (c *CheckAlias) run(stopCh chan struct{}) {
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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c.stopWg.Add(1)
defer c.stopWg.Done()
// If we have a specific node set, then use a blocking query
if c.Node != "" {
c.runQuery(stopCh)
return
}
// Use the local state to match the service.
c.runLocal(stopCh)
}
func (c *CheckAlias) runLocal(stopCh chan struct{}) {
// Very important this is buffered as 1 so that we do not lose any
// queued updates. This only has to be exactly 1 since the existence
// of any update triggers us to load the full health check state.
notifyCh := make(chan struct{}, 1)
c.Notify.AddAliasCheck(c.CheckID, c.ServiceID, notifyCh)
defer c.Notify.RemoveAliasCheck(c.CheckID, c.ServiceID)
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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// maxDurationBetweenUpdates is maximum time we go between explicit
// notifications before we re-query the aliased service checks anyway. This
// helps in the case we miss an edge triggered event and the alias does not
// accurately reflect the underlying service health status.
const maxDurationBetweenUpdates = 1 * time.Minute
var refreshTimer <-chan time.Time
extendRefreshTimer := func() {
refreshTimer = time.After(maxDurationBetweenUpdates)
}
updateStatus := func() {
checks := c.Notify.Checks(structs.WildcardEnterpriseMeta())
checksList := make([]*structs.HealthCheck, 0, len(checks))
for _, chk := range checks {
checksList = append(checksList, chk)
}
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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c.processChecks(checksList)
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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extendRefreshTimer()
}
// Immediately run to get the current state of the target service
updateStatus()
for {
select {
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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case <-refreshTimer:
updateStatus()
case <-notifyCh:
updateStatus()
case <-stopCh:
return
}
}
}
func (c *CheckAlias) runQuery(stopCh chan struct{}) {
args := c.RPCReq
args.Node = c.Node
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args.AllowStale = true
args.MaxQueryTime = 1 * time.Minute
args.EnterpriseMeta = c.EnterpriseMeta
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var attempt uint
for {
// Check if we're stopped. We fallthrough and block otherwise,
// which has a maximum time set above so we'll always check for
// stop within a reasonable amount of time.
select {
case <-stopCh:
return
default:
}
// Backoff if we have to
if attempt > checkAliasBackoffMin {
shift := attempt - checkAliasBackoffMin
if shift > 31 {
shift = 31 // so we don't overflow to 0
}
waitTime := (1 << shift) * time.Second
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if waitTime > checkAliasBackoffMaxWait {
waitTime = checkAliasBackoffMaxWait
}
time.Sleep(waitTime)
}
// Get the current health checks for the specified node.
//
// NOTE(mitchellh): This currently returns ALL health checks for
// a node even though we also have the service ID. This can be
// optimized if we introduce a new RPC endpoint to filter both,
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// but for blocking queries isn't that much more efficient since the checks
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// index is global to the cluster.
var out structs.IndexedHealthChecks
if err := c.RPC.RPC("Health.NodeChecks", &args, &out); err != nil {
attempt++
if attempt > 1 {
c.Notify.UpdateCheck(c.CheckID, api.HealthCritical,
fmt.Sprintf("Failure checking aliased node or service: %s", err))
}
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continue
}
attempt = 0 // Reset the attempts so we don't backoff the next
// Set our index for the next request
args.MinQueryIndex = out.Index
// We want to ensure that we're always blocking on subsequent requests
// to avoid hot loops. Index 1 is always safe since the min raft index
// is at least 5. Note this shouldn't happen but protecting against this
// case is safer than a 100% CPU loop.
if args.MinQueryIndex < 1 {
args.MinQueryIndex = 1
}
c.processChecks(out.HealthChecks)
}
}
// processChecks is a common helper for taking a set of health checks and
// using them to update our alias. This is abstracted since the checks can
// come from both the remote server as well as local state.
func (c *CheckAlias) processChecks(checks []*structs.HealthCheck) {
health := api.HealthPassing
msg := "No checks found."
for _, chk := range checks {
if c.Node != "" && chk.Node != c.Node {
continue
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}
// We allow ServiceID == "" so that we also check node checks
sid := chk.CompoundServiceID()
if chk.ServiceID != "" && !c.ServiceID.Matches(&sid) {
continue
}
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if chk.Status == api.HealthCritical || chk.Status == api.HealthWarning {
health = chk.Status
msg = fmt.Sprintf("Aliased check %q failing: %s", chk.Name, chk.Output)
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// Critical checks exit the for loop immediately since we
// know that this is the health state. Warnings do not since
// there may still be a critical check.
if chk.Status == api.HealthCritical {
break
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}
}
msg = "All checks passing."
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}
agent: fix several data races and bugs related to node-local alias checks (#5876) The observed bug was that a full restart of a consul datacenter (servers and clients) in conjunction with a restart of a connect-flavored application with bring-your-own-service-registration logic would very frequently cause the envoy sidecar service check to never reflect the aliased service. Over the course of investigation several bugs and unfortunate interactions were corrected: (1) local.CheckState objects were only shallow copied, but the key piece of data that gets read and updated is one of the things not copied (the underlying Check with a Status field). When the stock code was run with the race detector enabled this highly-relevant-to-the-test-scenario field was found to be racy. Changes: a) update the existing Clone method to include the Check field b) copy-on-write when those fields need to change rather than incrementally updating them in place. This made the observed behavior occur slightly less often. (2) If anything about how the runLocal method for node-local alias check logic was ever flawed, there was no fallback option. Those checks are purely edge-triggered and failure to properly notice a single edge transition would leave the alias check incorrect until the next flap of the aliased check. The change was to introduce a fallback timer to act as a control loop to double check the alias check matches the aliased check every minute (borrowing the duration from the non-local alias check logic body). This made the observed behavior eventually go away when it did occur. (3) Originally I thought there were two main actions involved in the data race: A. The act of adding the original check (from disk recovery) and its first health evaluation. B. The act of the HTTP API requests coming in and resetting the local state when re-registering the same services and checks. It took awhile for me to realize that there's a third action at work: C. The goroutines associated with the original check and the later checks. The actual sequence of actions that was causing the bad behavior was that the API actions result in the original check to be removed and re-added _without waiting for the original goroutine to terminate_. This means for brief windows of time during check definition edits there are two goroutines that can be sending updates for the alias check status. In extremely unlikely scenarios the original goroutine sees the aliased check start up in `critical` before being removed but does not get the notification about the nearly immediate update of that check to `passing`. This is interlaced wit the new goroutine coming up, initializing its base case to `passing` from the current state and then listening for new notifications of edge triggers. If the original goroutine "finishes" its update, it then commits one more write into the local state of `critical` and exits leaving the alias check no longer reflecting the underlying check. The correction here is to enforce that the old goroutines must terminate before spawning the new one for alias checks.
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// TODO(rb): if no matching checks found should this default to critical?
// Update our check value
c.Notify.UpdateCheck(c.CheckID, health, msg)
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}