linux_patch_manager/tasks/todo.md

Target Host for Service Health Checks

Overview

Add target_host_id field to service health checks, allowing a check configured on Host A to query a service on Host B's agent. Useful for redundant services running on multiple machines.

Design: target_host_id is nullable. When NULL (default), behavior unchanged — check queries its own host's agent. When set, the service check queries the target host's agent instead. Only applies to service checks; HTTP checks already specify a full URL.

Implementation Checklist

1. Database Migration

• Create migrations/011_health_check_target_host.sql
• Add target_host_id UUID REFERENCES hosts(id) ON DELETE SET NULL column
• Add partial index on target_host_id where NOT NULL

2. Backend Models (crates/pm-core/src/models.rs)

• Add target_host_id: Option<Uuid> to HealthCheck struct
• Add target_host_id: Option<Uuid> to CreateHealthCheckRequest
• Add target_host_id: Option<Uuid> to UpdateHealthCheckRequest
• Add target_host_id to all HealthCheck SELECT queries

3. API Routes (crates/pm-web/src/routes/health_checks.rs)

• Create: add target_host_id to INSERT, validate target host exists + is healthy
• Update: add target_host_id to COALESCE UPDATE
• List/Get: add target_host_id to SELECT columns
• Test endpoint (run_service_check): when target_host_id is Some, query that host's IP/port
• Audit log: include target_host_id in audit JSON

4. Health Check Poller (crates/pm-worker/src/health_check_poller.rs)

• Add target_host_id: Option<Uuid> to HealthCheckRow
• Modify SQL: LEFT JOIN hosts th ON th.id = hc.target_host_id, use COALESCE(th.ip_address, h.ip_address) and COALESCE(th.agent_port, h.agent_port)
• Add target_ip_address and target_agent_port fields to HealthCheckRow
• run_service_check: use target host IP/port when available
• check_host_health_checks: no change needed (results count toward owning host)

5. Frontend Types (frontend/src/types/index.ts)

• Add target_host_id?: string to HealthCheck
• Add target_host_id?: string to CreateHealthCheckRequest
• Add target_host_id?: string to UpdateHealthCheckRequest

6. Frontend Form (frontend/src/pages/HostDetailPage.tsx)

• Add target_host_id: string to HealthCheckFormValues
• Add target_host_id: '' to defaultHealthCheckForm
• Add host selector dropdown in HealthCheckFormDialog (visible when check_type === 'service')
• Fetch hosts list for dropdown (use hostsApi.list or a dedicated endpoint)
• handleHcCreateSubmit: include target_host_id: values.target_host_id || undefined
• handleHcEditClick: map check.target_host_id ?? '' to form
• handleHcEditSubmit: include target_host_id in UpdateHealthCheckRequest
• Display target host in health checks table Target column

7. Build, Test, Deploy

• Run cargo fmt --all + cargo clippy + cargo test
• Run frontend build + ESLint + tsc
• Commit and push through CI pipeline
• Tag release, build .deb, deploy to dev

Design Decisions

• target_host_id is nullable — NULL = check own host (backward compatible)
• FK with ON DELETE SET NULL — if target host deleted, revert to default
• Only applies to service checks (HTTP checks already have full URL)
• Health gate: results count toward the owning host, not the target host
• No RBAC required for target host — only requirement: target host exists in manager and is currently healthy