Aurora SLA Measurement

Overview

The primary goal of the feature is collection and monitoring of Aurora job SLA (Service Level Agreements) metrics that defining a contractual relationship between the Aurora/Mesos platform and hosted services.

The Aurora SLA feature currently supports stat collection only for service (non-cron) production jobs ("production = True" in your .aurora config).

Counters that track SLA measurements are computed periodically within the scheduler. The individual instance metrics are refreshed every minute (configurable via sla_stat_refresh_interval). The instance counters are subsequently aggregated by relevant grouping types before exporting to scheduler /vars endpoint (when using vagrant that would be http://192.168.33.7:8081/vars)

Metric Details

Platform Uptime

Aggregate amount of time a job spends in a non-runnable state due to platform unavailability or scheduling delays. This metric tracks Aurora/Mesos uptime performance and reflects on any system-caused downtime events (tasks LOST or DRAINED). Any user-initiated task kills/restarts will not degrade this metric.

Collection scope:

  • Per job - sla_<job_key>_platform_uptime_percent
  • Per cluster - sla_cluster_platform_uptime_percent

Units: percent

A fault in the task environment may cause the Aurora/Mesos to have different views on the task state or lose track of the task existence. In such cases, the service task is marked as LOST and rescheduled by Aurora. For example, this may happen when the task stays in ASSIGNED or STARTING for too long or the Mesos slave becomes unhealthy (or disappears completely). The time between task entering LOST and its replacement reaching RUNNING state is counted towards platform downtime.

Another example of a platform downtime event is the administrator-requested task rescheduling. This happens during planned Mesos slave maintenance when all slave tasks are marked as DRAINED and rescheduled elsewhere.

To accurately calculate Platform Uptime, we must separate platform incurred downtime from user actions that put a service instance in a non-operational state. It is simpler to isolate user-incurred downtime and treat all other downtime as platform incurred.

Currently, a user can cause a healthy service (task) downtime in only two ways: via killTasks or restartShards RPCs. For both, their affected tasks leave an audit state transition trail relevant to uptime calculations. By applying a special “SLA meaning” to exposed task state transition records, we can build a deterministic downtime trace for every given service instance.

A task going through a state transition carries one of three possible SLA meanings (see SlaAlgorithm.java) for sla-to-task-state mapping):

  • Task is UP: starts a period where the task is considered to be up and running from the Aurora platform standpoint.

  • Task is DOWN: starts a period where the task cannot reach the UP state for some non-user-related reason. Counts towards instance downtime.

  • Task is REMOVED from SLA: starts a period where the task is not expected to be UP due to user initiated action or failure. We ignore this period for the uptime calculation purposes.

This metric is recalculated over the last sampling period (last minute) to account for any UP/DOWN/REMOVED events. It ignores any UP/DOWN events not immediately adjacent to the sampling interval as well as adjacent REMOVED events.

Job Uptime

Percentage of the job instances considered to be in RUNNING state for the specified duration relative to request time. This is a purely application side metric that is considering aggregate uptime of all RUNNING instances. Any user- or platform initiated restarts directly affect this metric.

Collection scope: We currently expose job uptime values at 5 pre-defined percentiles (50th,75th,90th,95th and 99th):

  • sla_<job_key>_job_uptime_50_00_sec
  • sla_<job_key>_job_uptime_75_00_sec
  • sla_<job_key>_job_uptime_90_00_sec
  • sla_<job_key>_job_uptime_95_00_sec
  • sla_<job_key>_job_uptime_99_00_sec

Units: seconds You can also get customized real-time stats from aurora client. See aurora sla -h for more details.

Median Time To Assigned (MTTA)

Median time a job spends waiting for its tasks to be assigned to a host. This is a combined metric that helps track the dependency of scheduling performance on the requested resources (user scope) as well as the internal scheduler bin-packing algorithm efficiency (platform scope).

Collection scope:

  • Per job - sla_<job_key>_mtta_ms
  • Per cluster - sla_cluster_mtta_ms
  • Per instance size (small, medium, large, x-large, xx-large). Size are defined in: ResourceAggregates.java)
    • By CPU:
    • sla_cpu_small_mtta_ms
    • sla_cpu_medium_mtta_ms
    • sla_cpu_large_mtta_ms
    • sla_cpu_xlarge_mtta_ms
    • sla_cpu_xxlarge_mtta_ms
    • By RAM:
    • sla_ram_small_mtta_ms
    • sla_ram_medium_mtta_ms
    • sla_ram_large_mtta_ms
    • sla_ram_xlarge_mtta_ms
    • sla_ram_xxlarge_mtta_ms
    • By DISK:
    • sla_disk_small_mtta_ms
    • sla_disk_medium_mtta_ms
    • sla_disk_large_mtta_ms
    • sla_disk_xlarge_mtta_ms
    • sla_disk_xxlarge_mtta_ms

Units: milliseconds

MTTA only considers instances that have already reached ASSIGNED state and ignores those that are still PENDING. This ensures straggler instances (e.g. with unreasonable resource constraints) do not affect metric curves.

Median Time To Running (MTTR)

Median time a job waits for its tasks to reach RUNNING state. This is a comprehensive metric reflecting on the overall time it takes for the Aurora/Mesos to start executing user content.

Collection scope:

  • Per job - sla_<job_key>_mttr_ms
  • Per cluster - sla_cluster_mttr_ms
  • Per instance size (small, medium, large, x-large, xx-large). Size are defined in: ResourceAggregates.java)
    • By CPU:
    • sla_cpu_small_mttr_ms
    • sla_cpu_medium_mttr_ms
    • sla_cpu_large_mttr_ms
    • sla_cpu_xlarge_mttr_ms
    • sla_cpu_xxlarge_mttr_ms
    • By RAM:
    • sla_ram_small_mttr_ms
    • sla_ram_medium_mttr_ms
    • sla_ram_large_mttr_ms
    • sla_ram_xlarge_mttr_ms
    • sla_ram_xxlarge_mttr_ms
    • By DISK:
    • sla_disk_small_mttr_ms
    • sla_disk_medium_mttr_ms
    • sla_disk_large_mttr_ms
    • sla_disk_xlarge_mttr_ms
    • sla_disk_xxlarge_mttr_ms

Units: milliseconds

MTTR only considers instances in RUNNING state. This ensures straggler instances (e.g. with unreasonable resource constraints) do not affect metric curves.

Limitations

  • The availability of Aurora SLA metrics is bound by the scheduler availability.

  • All metrics are calculated at a pre-defined interval (currently set at 1 minute). Scheduler restarts may result in missed collections.