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Worker health - Temporal Cloud feature guide

This page is a guide to monitoring a Temporal Worker fleet and covers the following scenarios:

Minimal Observations​

These alerts should be configured and understood first to gain intelligence into your application health and behaviors.

  1. Create monitors and alerts for Schedule-To-Start latency SDK metrics (both Workflow Executions and Activity Executions). See Detect Task backlog section to explore sample queries and appropriate responses that accompany these values.
  • Alert at >200ms for your p99 value
  • Plot >100ms for your p95 value
  1. Create a Grafana panel called Sync Match Rate. See the Sync Match Rate section to explore example queries and appropriate responses that accompany these values.
  • Alert at <95% for your p99 value
  • Plot <99% for your p95 value
  1. Create a Grafana panel called Poll Success Rate. See the Detect greedy Workers section for example queries and appropriate responses that accompany these values.
  • Alert at <90% for your p99 value
  • Plot <95% for your p95 value

The following alerts build on the above to dive deeper into specific potential causes for Worker related issues you might be experiencing.

  1. Create monitors and alerts for the temporal_worker_task_slots_available SDK metric. See the Detect misconfigured Workers section for appropriate responses based on the value.
  • Alert at 0 for your p99 value
  1. Create monitors for the temporal_sticky_cache_size SDK metric. See the Configure Sticky Cache section for more details on this configuration.
  • Plot at {value} > {WorkflowCacheSize.Value}
  1. Create monitors for the temporal_sticky_cache_total_forced_eviction SDK metric. This metric is available in the Go SDK, and the Java SDK only. See the Configure Sticky Cache section for more details and appropriate responses.
  • Alert at >{predetermined_high_number}

Detect Task Backlog​

How to detect a backlog of Tasks.

Metrics to monitor:

Schedule To Start latency​

The Schedule-To-Start metric represents how long Tasks are staying unprocessed, in the Task Queues. But differently, it is the time between when a Task is enqueued and when it is picked up by a Worker. This time being long (likely) means that your Workers can't keep up — either increase the number of Workers (if the host load is already high) or increase the number of pollers per Worker.

If your Schedule-To-Start latency alert triggers or is high, check the Sync Match Rate to decide if you need to adjust your Worker or fleet, or contact Temporal Cloud support. If your Sync Match Rate is low, contact Temporal Cloud support. If your Sync Match Rate is low, you can contact Temporal Cloud support.

The schedule_to_start_latency SDK metric for both Workflow Executions and Activity Executions should have alerts.

Prometheus query samples​

Workflow Task Latency, 99th percentile

histogram_quantile(0.99, sum(rate(temporal_workflow_task_schedule_to_start_latency_seconds_bucket[5m])) by (le, namespace, task_queue))

Workflow Task Latency, average

sum(increase(temporal_workflow_task_schedule_to_start_latency_seconds_sum[5m])) by (namespace, task_queue)
/
sum(increase(temporal_workflow_task_schedule_to_start_latency_seconds_count[5m])) by (namespace, task_queue)

Activity Task Latency, 99th percentile

histogram_quantile(0.99, sum(rate(temporal_activity_schedule_to_start_latency_seconds_bucket[5m])) by (le, namespace, task_queue))

Activity Task Latency, average

sum(increase(temporal_activity_schedule_to_start_latency_seconds_sum[5m])) by (namespace, task_queue)
/
sum(increase(temporal_activity_schedule_to_start_latency_seconds_count[5m])) by (namespace, task_queue)

Target

This latency should be very low, close to zero. Any higher value indicates a bottleneck. Anything else indicates bottlenecking.

Sync Match Rate​

The Sync Match Rate measures the proportion of Tasks that are delivered directly to Stickied Cached Workflows on Workers, compared to the total number of delivered Tasks.

A sync match is when a task is immediately matched to a Stickied Cached Workflow on a Worker.

An async match is when a Task cannot be matched to the Sticky Queue for a Worker. This can happen when no Worker has cached the Workflow, or if the Task times out during processing. In this case, the Task returns to the general Task Queue.

Calculate Sync Match Rate

temporal_cloud_v0_poll_success_sync_count ÷ temporal_cloud_v0_poll_success_count = N

Prometheus query samples​

sync_match_rate query

sum by(temporal_namespace) (
    rate(
        temporal_cloud_v0_poll_success_sync_count{temporal_namespace=~"$namespace"}[5m]
    )
)
/
sum by(temporal_namespace) (
    rate(
        temporal_cloud_v0_poll_success_count{temporal_namespace=~"$namespace"}[5m]
    )
)

Target

The Sync Match Rate should be at least >95%, but preferably >99%.

Interpretation

Consider if this acceptable for your use case to have low Sync Match Rate. For example, if you have known workloads or you intentionally throttle tasks.

If Schedule-To-Start latencies are high, the Task Queue is experiencing a backlog of Tasks.

It's also important to understand the fill and drain rates of the async tasks are during these windows:

Successful async polls

temporal_cloud_v0_poll_success_count - temporal_cloud_v0_poll_success_sync_count = N
sum(rate(temporal_cloud_v0_poll_success_count{temporal_namespace=~"$temporal_namespace"}[5m])) by (temporal_namespace, task_type)
-
sum(rate(temporal_cloud_v0_poll_success_sync_count{temporal_namespace=~"$temporal_namespace"}[5m])) by (temporal_namespace, task_type)

Actions

  • Verify that your Worker setup is optimized for your instance:
    • Check the system CPU usage against task_slots and adjust maxConcurrentWorkflowTaskExecutionSize and maxConcurrentActivityExecutionSize settings as necessary.
    • Check the system memory usage against sticky_cache_size and adjust sticky cache size as necessary.
    • For a detailed explanation of settings, see the Worker Performance section.
  • Increase the Worker config for concurrent pollers for Workflow or Activity task_slots, if your Worker resources can accommodate the increased load.
  • Increase the number of available Workers.
danger

Setting the Schedule-To-Start Timeout in your Activity Options can skew your observations. Avoid setting a Schedule-To-Start Timeout when load testing for latency.

Detect greedy Worker resources​

How to detect greedy Worker resources.

You can have too many Workers. If you see the Poll Success Rate showing low numbers, you might have too many resources polling Temporal Cloud.

Metrics to monitor:

Calculate Poll Success Rate

(temporal_cloud_v0_poll_success_count + temporal_cloud_v0_poll_success_sync_count)
/
(temporal_cloud_v0_poll_success_count + temporal_cloud_v0_poll_success_sync_count + temporal_cloud_v0_poll_timeout_count)

Target

Poll Success Rate should be >90% in most cases of systems with a steady load. For high volume and low latency, try to target >95%.

Interpretation

There may be too many Pollers for the amount of Workers.

If you see the following at the same time then you might have too many Workers:

  • ResourceExhausted on poll operations, e.g. temporal_long_request_failure{operation=~"Poll.*"}
  • Low poll success rate

Actions

Consider sizing down your Workers by either:

  • Reducing the number of Workers polling the impacted Task Queue, OR
  • Reducing the concurrent pollers per Worker, OR
  • Both of the above

Prometheus query samples​

poll_success_rate query

(
    (
        sum by(temporal_namespace) (
          rate(
            temporal_cloud_v0_poll_success_count{temporal_namespace=~"$namespace"}[5m]
          )
        )
      +
        sum by(temporal_namespace) (
          rate(
            temporal_cloud_v0_poll_success_sync_count{temporal_namespace=~"$namespace"}[5m]
          )
        )
    )
  /
    (
        (
            sum by(temporal_namespace) (
              rate(
                temporal_cloud_v0_poll_success_count{temporal_namespace=~"$namespace"}[5m]
              )
            )
          +
            sum by(temporal_namespace) (
              rate(
                temporal_cloud_v0_poll_success_sync_count{temporal_namespace=~"$namespace"}[5m]
              )
            )
        )
      +
        sum by(temporal_namespace) (
          rate(
            temporal_cloud_v0_poll_timeout_count{temporal_namespace=~"$namespace"}[5m]
          )
        )
    )
)

Detect misconfigured Workers​

How to detect misconfigured Workers.

Worker configuration can negatively affect Task processing efficiency.

Metrics to monitor:

Execution Size Configuration

The maxConcurrentWorkflowTaskExecutionSize and maxConcurrentActivityExecutionSize define the number of total available slots for the Worker. If this is set too low, the Worker will not be able to keep up processing Tasks.

Target

The temporal_worker_task_slots_available metric should always be >0.

Prometheus query samples​

Over Time

avg_over_time(temporal_worker_task_slots_available{namespace="$namespace",worker_type="WorkflowWorker"}[10m])

Current Time

temporal_worker_task_slots_available{namespace="default", worker_type="WorkflowWorker", task_queue="$task_queue_name"}

Interpretation

You are likely experiencing a Task backlog if you are seeing inadequate slot counts frequently. The work is not getting processed as fast as it should/can.

Action

Increase the maxConcurrentWorkflowTaskExecutionSize and maxConcurrentActivityExecutionSize values and keep an eye on your Worker resource metrics (CPU utilization, etc) to make sure you haven't created a new issue.

Configure Sticky Execution Cache​

Sticky Execution means that a Worker caches a Workflow Execution Event History and creates a dedicated Task Queue to listen on. It significantly improves performance because the Temporal Service only sends new events to the Worker instead of entire Event Histories.

How to configure your Workflow Sticky cache.

The WorkflowCacheSize should always be greater than the sticky_cache_size metric value. Additionally, you can watch sticky_cache_total_forced_eviction for unusually high numbers that are likely an indicator of inefficiency, since Workflows are being evicted from the cache.

Target

The sticky_cache_size should report less than or equal to your WorkflowCacheSize value. Also, sticky_cache_total_forced_eviction should not be reporting high numbers (relative).

Action

If you see a high eviction count, verify there are no other inefficiencies in your Worker configuration or resource provisioning (backlog). If you see the cache size metric exceed the WorkflowCacheSize, increase this value if your Worker resources can accommodate it or provision more Workers. Finally, take time to review this document and see if it addresses other potential cache issues.

Prometheus query samples​

Sticky Cache Size

max_over_time(temporal_sticky_cache_size{namespace="$namespace"}[10m])

Sticky Cache Evictions

rate(temporal_sticky_cache_total_forced_eviction_total{namespace="$namespace"}[5m]))