Mapping API gateways to distributed GIS endpoints

In a federated geospatial data mesh, routing failures originate from misaligned ingress resolution, not network partitioning. The operational mandate is deterministic header-based routing, strict schema validation, and bounded circuit breakers. This configuration eliminates cross-domain fan-out latency, enforces domain ownership boundaries, and guarantees predictable p99 response times under heavy spatial query loads.

Operational Routing Topology

Route resolution must decouple ingress evaluation from backend dispatch. Spatial context headers (X-Spatial-Domain, X-Vector-Schema, X-Query-Weight) serve as the authoritative routing vector. The header evaluation layer must align with API Gateway Mapping for GIS Services to ensure domain-specific payloads are directed to bounded contexts without cross-tenant leakage. This routing topology directly depends on established architectural contracts and operates within the broader Federated Ownership & Routing Architecture, where domain boundaries dictate retry budgets, timeout thresholds, and fallback chains.

Declarative Configuration & Header Resolution

The following Envoy RouteConfiguration enforces deterministic spatial routing, header matching, and circuit breaker thresholds. The configuration is structured for Envoy v3 compliance and idempotent deployment via GitOps pipelines.

yaml
static_resources:
  listeners:
  - name: gis_ingress
    address:
      socket_address:
        address: 0.0.0.0
        port_value: 8080
    filter_chains:
    - filters:
      - name: envoy.filters.network.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          stat_prefix: gis_mesh
          access_log:
          - name: envoy.access_loggers.file
            typed_config:
              "@type": type.googleapis.com/envoy.extensions.access_loggers.file.v3.FileAccessLog
              path: /var/log/envoy/gis_access.log
              log_format:
                text_format: "[%START_TIME%] %REQ(:METHOD)% %REQ(X-ENVOY-ORIGINAL-PATH?:PATH)% %PROTOCOL% %RESPONSE_CODE% %RESPONSE_FLAGS% %UPSTREAM_HOST% %REQ(X-SPATIAL-DOMAIN)% %REQ(X-QUERY-WEIGHT)%\n"
          route_config:
            name: spatial_routing
            virtual_hosts:
            - name: tile_vector_domains
              domains: ["*"]
              routes:
              - match:
                  prefix: "/v1/tiles/"
                  headers:
                  - name: "X-Spatial-Domain"
                    exact_match: "cadastral"
                route:
                  cluster: cadastral_tile_cluster
                  timeout: 2.5s
                  retry_policy:
                    retry_on: "5xx,reset,connect-failure"
                    num_retries: 1
              - match:
                  prefix: "/v1/geocode/"
                  headers:
                  - name: "X-Query-Weight"
                    regex_match: "^heavy$"
                route:
                  cluster: async_spatial_worker_cluster
                  timeout: 15.0s
                  retry_policy:
                    retry_on: "5xx"
                    num_retries: 0
  clusters:
  - name: cadastral_tile_cluster
    connect_timeout: 1.0s
    circuit_breakers:
      thresholds:
      - max_connections: 500
        max_pending_requests: 300
        max_requests: 800
        max_retries: 2
    load_assignment:
      cluster_name: cadastral_tile_cluster
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: cadastral-gis.internal
                port_value: 443
  - name: async_spatial_worker_cluster
    connect_timeout: 2.0s
    circuit_breakers:
      thresholds:
      - max_connections: 200
        max_pending_requests: 100
        max_requests: 400
        max_retries: 0
    load_assignment:
      cluster_name: async_spatial_worker_cluster
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: spatial-async-worker.internal
                port_value: 8443

Schema Validation & Idempotent Execution

Spatial payloads require strict contract enforcement before dispatch. Implement a pre-routing validation filter that rejects malformed X-Vector-Schema headers against OGC-compliant tile/vector specifications. Reference the official OGC API - Tiles standard for bounding box normalization and coordinate reference system (CRS) validation.

Idempotent execution is enforced via the Idempotency-Key header, which must be derived from a normalized spatial query hash (SHA-256 of bbox + crs + layer_id + timestamp_window). The gateway caches this key in a distributed Redis cluster with a TTL matching the upstream query execution window. Duplicate requests within the TTL return 200 OK with the cached payload, preventing redundant compute cycles and upstream saturation. Heavy spatial queries (X-Query-Weight: heavy) are routed to asynchronous workers with num_retries: 0 to prevent cascading retry storms.

Diagnostic Log Patterns & Telemetry

Gateway telemetry must capture routing decisions, circuit breaker state transitions, and upstream failures. Monitor the following exact log patterns in /var/log/envoy/gis_access.log:

Pattern Severity Root Cause Remediation
RESPONSE_FLAGS=UF Critical Upstream connection refused Verify TLS handshake, health check endpoint, and DNS resolution for cadastral-gis.internal
RESPONSE_FLAGS=UT High Upstream timeout (>2.5s) Check spatial query complexity, index fragmentation, or worker thread exhaustion
RESPONSE_FLAGS=UO High Circuit breaker open Reduce concurrent spatial requests, scale backend horizontally, or adjust max_connections threshold
RESPONSE_FLAGS=NR Medium No route matched Validate X-Spatial-Domain header casing and exact match regex alignment
RESPONSE_FLAGS=DC Low Downstream client disconnect Optimize payload streaming or enforce client-side timeout alignment

Enable Envoy’s envoy.upstream_rq_timeout and envoy.cluster.circuit_breakers metrics in Prometheus. Alert when circuit_breaker_open exceeds 3 consecutive windows or when p99_latency breaches 2.2s on tile endpoints.

Incident Escalation & Recovery Paths

Operational response follows a strict tiered escalation matrix. All actions must be idempotent and reversible via configuration rollback.

Tier 1: Gateway Configuration Drift (0–15 min)

  • Verify route matcher syntax against deployed Envoy config dump (curl -s localhost:15000/config_dump | jq '.configs[] | select(.type == "envoy.config.route.v3.RouteConfiguration")')
  • Reconcile header routing rules with the latest GitOps commit.
  • Force a fresh config pull by restarting the gateway pods (Envoy has no admin reload endpoint; configuration is re-pulled via xDS on restart): kubectl rollout restart deploy/<gateway-deployment> -n geospatial-mesh

Tier 2: Upstream Schema Mismatch / Circuit Saturation (15–45 min)

  • Isolate affected domain by injecting X-Spatial-Domain: quarantine header routing to a shadow cluster.
  • Validate upstream OGC tile/vector contracts using schema registry diff tools.
  • Temporarily increase max_pending_requests by 20% while upstream scales, but enforce strict backpressure via Retry-After headers.

Tier 3: Mesh Partition / Fallback Chain Activation (45+ min)

  • Activate cross-domain fallback routing: reroute /v1/geocode/ to a cached, read-only geocoding replica.
  • Enable X-Query-Weight: degraded routing to bypass heavy compute paths.
  • Execute disaster recovery runbook: restore last known good Envoy snapshot, drain active connections, and validate spatial mesh partition health via distributed consensus checks.

All routing changes must pass pre-deployment validation against a staging mesh with synthetic spatial payloads. Post-incident, conduct a blameless post-mortem focusing on header contract drift, circuit breaker threshold calibration, and idempotency key collision rates.