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traefik/provider/marathon/readiness.go

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package marathon
import (
"time"
"github.com/containous/traefik/log"
marathon "github.com/gambol99/go-marathon"
)
const (
// readinessCheckDefaultTimeout is the default timeout for a readiness
// check if no check timeout is specified on the application spec. This
// should really never be the case, but better be safe than sorry.
readinessCheckDefaultTimeout = 10 * time.Second
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// readinessCheckSafetyMargin is some buffer duration to account for
// small offsets in readiness check execution.
readinessCheckSafetyMargin = 5 * time.Second
readinessLogHeader = "Marathon readiness check: "
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)
type readinessChecker struct {
checkDefaultTimeout time.Duration
checkSafetyMargin time.Duration
traceLogging bool
}
func defaultReadinessChecker(isTraceLogging bool) *readinessChecker {
return &readinessChecker{
checkDefaultTimeout: readinessCheckDefaultTimeout,
checkSafetyMargin: readinessCheckSafetyMargin,
traceLogging: isTraceLogging,
}
}
func (rc *readinessChecker) Do(task marathon.Task, app marathon.Application) bool {
if rc == nil {
// Readiness checker disabled.
return true
}
switch {
case len(app.Deployments) == 0:
// We only care about readiness during deployments; post-deployment readiness
// can be covered by a periodic post-deployment probe (i.e., Traefik health checks).
rc.tracef("task %s app %s: ready = true [no deployment ongoing]", task.ID, app.ID)
return true
case app.ReadinessChecks == nil || len(*app.ReadinessChecks) == 0:
// Applications without configured readiness checks are always considered
// ready.
rc.tracef("task %s app %s: ready = true [no readiness checks on app]", task.ID, app.ID)
return true
}
// Loop through all readiness check results and return the results for
// matching task IDs.
if app.ReadinessCheckResults != nil {
for _, readinessCheckResult := range *app.ReadinessCheckResults {
if readinessCheckResult.TaskID == task.ID {
rc.tracef("task %s app %s: ready = %t [evaluating readiness check ready state]", task.ID, app.ID, readinessCheckResult.Ready)
return readinessCheckResult.Ready
}
}
}
// There's a corner case sometimes hit where the first new task of a
// deployment goes from TASK_STAGING to TASK_RUNNING without a corresponding
// readiness check result being included in the API response. This only happens
// in a very short (yet unlucky) time frame and does not repeat for subsequent
// tasks of the same deployment.
// Complicating matters, the situation may occur for both initially deploying
// applications as well as rolling-upgraded ones where one or more tasks from
// a previous deployment exist already and are joined by new tasks from a
// subsequent deployment. We must always make sure that pre-existing tasks
// maintain their ready state while newly launched tasks must be considered
// unready until a check result appears.
// We distinguish the two cases by comparing the current time with the start
// time of the task: It should take Marathon at most one readiness check timeout
// interval (plus some safety margin to account for the delayed nature of
// distributed systems) for readiness check results to be returned along the API
// response. Once the task turns old enough, we assume it to be part of a
// pre-existing deployment and mark it as ready. Note that it is okay to err
// on the side of caution and consider a task unready until the safety time
// window has elapsed because a newly created task should be readiness-checked
// and be given a result fairly shortly after its creation (i.e., on the scale
// of seconds).
readinessCheckTimeoutSecs := (*app.ReadinessChecks)[0].TimeoutSeconds
readinessCheckTimeout := time.Duration(readinessCheckTimeoutSecs) * time.Second
if readinessCheckTimeout == 0 {
rc.tracef("task %s app %s: readiness check timeout not set, using default value %s", task.ID, app.ID, rc.checkDefaultTimeout)
readinessCheckTimeout = rc.checkDefaultTimeout
} else {
readinessCheckTimeout += rc.checkSafetyMargin
}
startTime, err := time.Parse(time.RFC3339, task.StartedAt)
if err != nil {
// An unparseable start time should never occur; if it does, we assume the
// problem should be surfaced as quickly as possible, which is easiest if
// we shun the task from rotation.
log.Warnf("Failed to parse start-time %s of task %s from application %s: %s (assuming unready)", task.StartedAt, task.ID, app.ID, err)
return false
}
since := time.Since(startTime)
if since < readinessCheckTimeout {
rc.tracef("task %s app %s: ready = false [task with start-time %s not within assumed check timeout window of %s (elapsed time since task start: %s)]", task.ID, app.ID, startTime.Format(time.RFC3339), readinessCheckTimeout, since)
return false
}
// Finally, we can be certain this task is not part of the deployment (i.e.,
// it's an old task that's going to transition into the TASK_KILLING and/or
// TASK_KILLED state as new tasks' readiness checks gradually turn green.)
rc.tracef("task %s app %s: ready = true [task with start-time %s not involved in deployment (elapsed time since task start: %s)]", task.ID, app.ID, startTime.Format(time.RFC3339), since)
return true
}
func (rc *readinessChecker) tracef(format string, args ...interface{}) {
if rc.traceLogging {
log.Debugf(readinessLogHeader+format, args...)
}
}