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The Palyra scheduler is a centralized orchestration component within the palyrad daemon responsible for executing time-based workflows, system maintenance tasks, and periodic security audits. It manages the lifecycle of scheduled jobs, enforces concurrency and misfire policies, and integrates with the Cedar policy engine for job authorization.

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Scheduler Architecture

The scheduler operates as a background loop spawned during daemon initialization. It manages three primary categories of tasks:
  1. User-Defined Routines: Jobs scheduled via the Cron or Routines API (e.g., “Summarize health every 5 minutes”).
  2. Memory Maintenance: Periodic tasks for vector database optimization and embedding backfills.
  3. Security Audits: Background re-verification of installed WASM skills against the SkillTrustStore.

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Scheduler Loop Implementation

The core loop is defined in spawn_scheduler_loop within crates/palyra-daemon/src/cron.rs. It utilizes a tokio::sync::Notify mechanism to wake up either at the next scheduled job time or after a maximum idle sleep of 15 seconds crates/palyra-daemon/src/cron.rs#42-42.

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Code Entity Map: Scheduler Flow

The following diagram maps the natural language concepts of “Scheduling” to the specific Rust entities and data structures used in the implementation. Title: Scheduler Entity Mapping Sources: crates/palyra-daemon/src/cron.rs#121-137, crates/palyra-daemon/src/cron.rs#158-174, crates/palyra-daemon/src/journal.rs#35-40

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Schedule Normalization and Parsing

Palyra supports three types of schedules, which are normalized into a standard internal format using normalize_schedule crates/palyra-daemon/src/cron.rs#240-240.
Schedule TypeDescriptionCode Representation
CronStandard 5-field cron expression (min, hour, dom, month, dow).ParsedSchedule::Cron
EveryFixed interval execution (e.g., every 3600s).ParsedSchedule::Every
AtOne-off execution at a specific RFC3339 timestamp.ParsedSchedule::At

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Cron Matching Logic

The CronMatcher handles complex temporal logic, including support for both UTC and Local timezones crates/palyra-daemon/src/cron.rs#61-83. It implements next_after to calculate the subsequent execution window by iterating through minutes until a match is found, capped by MAX_CRON_LOOKAHEAD_MINUTES crates/palyra-daemon/src/cron.rs#46-46. Sources: crates/palyra-daemon/src/cron.rs#121-156, crates/palyra-daemon/src/cron.rs#158-174

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Job Dispatch and Policy Evaluation

When a job is due, the scheduler calls dispatch_job. This function performs several critical checks before initiating a run.

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Cedar Policy Evaluation

Before execution, the scheduler evaluates the job against the security policy using evaluate_with_context from palyra-policy crates/palyra-daemon/src/cron.rs#14-17. The PolicyRequestContext includes the SYSTEM_DAEMON_PRINCIPAL (“system:daemon”) and the specific routine metadata to ensure the scheduled task has the necessary permissions to invoke the requested tools crates/palyra-daemon/src/cron.rs#55-55.

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Execution Policies

The scheduler enforces two primary behavioral policies defined in the CronJobRecord:
  1. Concurrency Policy (CronConcurrencyPolicy):
    • Forbid: If a previous run is still active, the new run is skipped.
    • Replace: The active run is cancelled via OrchestratorCancelRequest before starting the new one.
    • QueueOne: (Internal) Queues a single pending execution.
  2. Misfire Policy (CronMisfirePolicy):
    • Skip: If the daemon was offline during a scheduled window, ignore the missed tick.
    • CatchUp: Execute the missed tick immediately upon daemon startup.
Sources: crates/palyra-daemon/src/cron.rs#35-40, crates/palyra-daemon/src/journal.rs#35-40

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Background System Tasks

Beyond user routines, the daemon executes internal maintenance tasks on fixed intervals.

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Memory Maintenance Ticks

The MemoryStore requires periodic housekeeping to maintain performance and accuracy:

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Skill Re-Audit Jobs

To protect against supply-chain attacks or local tampering, the scheduler performs periodic security re-audits of all installed WASM skills.
  • Interval: Default is 6 hours (DEFAULT_SKILL_REAUDIT_INTERVAL), configurable via PALYRA_SKILL_REAUDIT_INTERVAL_MS crates/palyra-daemon/src/cron.rs#53-54.
  • Logic: The scheduler iterates through the InstalledSkillsIndex, re-calculates the SHA-256 hash of the .palyra-skill artifact, and re-runs audit_skill_artifact_security crates/palyra-daemon/src/cron.rs#18-18. If a skill fails the audit, its status is updated to Quarantine in the SkillTrustStore.
Title: Background Task Dispatch Logic Sources: crates/palyra-daemon/src/cron.rs#27-40, crates/palyra-daemon/src/transport/http/handlers/console/routines.rs#154-162

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Configuration

Scheduler behavior is controlled via the cron and memory.retention sections of palyra.toml. 
[cron]
timezone = "local" # or "utc"

[memory.retention]
vacuum_schedule = "0 3 * * *" # Cron expression for DB optimization
ttl_days = 30
Sources: crates/palyra-common/src/daemon_config_schema.rs#133-135, crates/palyra-common/src/daemon_config_schema.rs#162-167