Synopsis

This chapter provides a practical checklist for multi-CDN programs. It maps objectives to design, security, origin, caching, telemetry, traffic steering, testing, rollout, and ongoing operations. Items are written to be auditable and printable. The aim is stable behavior, predictable costs, and clear ownership.

Objectives and scope

Document service objectives, success measures, and constraints. Define availability and latency targets per region. Record compliance and residency rules. Note content types, expected volumes, and seasonal peaks. Establish a decision owner for routing and for incidents. Record change control and rollback expectations.

Architecture and providers

Select the steering layer or layers that match constraints. DNS based steering is coarse and simple. Layer 7 proxy is reactive and flexible. Client side selection reflects last mile variance. Hybrid designs combine layers with defined precedence. Choose providers with sufficient footprint, observability, and contractual fit. Record known feature gaps and accepted workarounds.

Origin and shielding

Choose origin topology. Single origin with shielding suits read heavy traffic. Multi region origins reduce latency and allow isolation. Define addressing and host identity. Keep upstream Host and SNI stable. Deploy origin shielding with a clear boundary for caching and compression. Measure shield hit rate independently of edge hit rate.

Authentication and access

Protect origin paths. Apply IP allowlists where required. Prefer mutual TLS or signed headers for strong identity. Automate key and certificate rotation. Track token formats, issuers, and lifetimes. Verify time sources to avoid token skew. Keep administrative access least privilege with audit trails.

Cache identity and headers

Define canonical cache keys. Use scheme, host, normalized path, and a bounded set of query parameters. Use Vary only for headers that change bytes on the wire. Prefer immutable versioned asset URLs for static content. Set Cache-Control, ETag, and Last-Modified consistently. Align negative caching for error statuses.

Purge and consistency

Select purge methods per provider. Prefer soft purge with revalidation to reduce origin load. Build a purge controller that translates intent across APIs, tracks request ids, retries safely, and records outcomes. Sequence content publication before purges. Target bounded inconsistency windows and measure them.

TLS and protocols

Automate certificate issuance and renewal, preferably via ACME. Align protocol support and cipher policy across providers. Track OCSP stapling behavior. Decide on RSA, ECDSA, or dual stack. Enable HTTP/2 and HTTP/3 consistently where business requirements justify them. Document session resumption expectations.

Security parity

Maintain functionally equivalent WAF rules, bot defenses, rate limits, and exception handling across providers. Manage rules from a single source of truth with translation to vendor formats. Run periodic diffs and behavioral tests. Normalize logs to a common schema.

Telemetry and control plane

Collect real user and synthetic data. Segment by region, ASN, protocol, device class, and provider. Aggregate on windows that match steering cadence. Build a control plane that records inputs, decisions, and applied outputs. Provide safe defaults on signal loss. Publish schemas and window definitions.

Traffic steering policy

Define precedence: jurisdiction and allowlist, then health, then performance against objectives, then cost within guard rails. Add stability controls such as dwell times, dampening, and maximum exposure. Publish tie breaks. Record decisions with context for audits.

Testing and rollout

Validate configuration with static checks and simulations. Design stable cohorts for candidate vs control comparisons. Start with small exposure, hold, measure, and either increase or revert. Separate cold and warm cache phases when keys change. Annotate dashboards for each step.

Incident playbooks

Prepare playbooks for provider outage, regional degradation, cache collapse, purge failure, and certificate error. Scope by provider, region, and ASN. Prefer isolation within scope over global actions. Record every change and verification. Restore in reverse order when conditions improve.

Cost and contracts

Model spend by region and product. Choose commit levels that fit routing variability. Encode cost signals for policy only after health and performance. Reconcile invoices to measured usage. Record cost impact of incident pinning and large rollouts.

Compliance and residency

Express routing constraints per region. Keep raw logs and telemetry local where required and export only aggregated statistics without identifiers. Align key custody with jurisdiction. Test residency behavior with probes and storage audits. Record exceptions with scope and duration.

Documentation and ownership

Store policies, diagrams, and runbooks in version control. Assign owners for routing, origin, security, purge, telemetry, and cost. Review documents on a cadence. Track provider contacts and escalation paths.

Printable condensed checklist

[ ] Objectives defined: availability, latency, regions, compliance, owners
[ ] Architecture chosen: DNS / L7 proxy / client / hybrid with precedence
[ ] Providers selected: coverage, observability, feature gaps recorded
[ ] Origin topology set: single + shield / multi region; Host and SNI stable
[ ] Origin access: IP controls, mTLS or signed headers, rotation automated
[ ] Cache key documented: scheme, host, path, params; Vary minimal
[ ] Headers aligned: Cache-Control, ETag, Last-Modified, negative caching
[ ] Immutable asset strategy in place; versioned URLs used
[ ] Purge controller built: intent translation, retries, ids, audit
[ ] TLS automated: ACME, RSA/ECDSA plan, OCSP stapling verified
[ ] Protocols aligned: H2/H3 enabled as required; cipher policy matched
[ ] Security parity: WAF, bot, rate limits; normalized logs and tests
[ ] Telemetry pipelines: RUM + synthetic; windows and schema published
[ ] Control plane: inputs, decisions, outputs recorded; safe defaults
[ ] Steering policy: jurisdiction -> health -> performance -> cost
[ ] Stability controls: dwell times, dampening, exposure caps
[ ] Testing plan: cohorts, canary, cold/warm phases, annotations
[ ] Rollout gates: objectives and error budgets defined
[ ] Playbooks: outage, regional degradation, cache, purge, cert issues
[ ] Cost model: commits, overage, reconciliation, incident cost notes
[ ] Residency controls: routing, logging, key custody, audits
[ ] Ownership and review cadence documented

Overview appears at /multicdn/. Design choices appear in /multicdn/architecture-patterns/. Routing rules appear in /multicdn/traffic-steering/. Origin and caching details appear in /multicdn/origin-architecture/ and /multicdn/cache-consistency/. Telemetry and operations appear in /multicdn/signals-telemetry/ and /multicdn/monitoring-slos/. Incident handling appears in /multicdn/incident-playbooks/. Commercial topics appear in /multicdn/cost-contracts/. Compliance appears in /multicdn/compliance/.

Further reading

RFC 9110 and RFC 9111 for HTTP semantics and caching. RFC 8446 for TLS 1.3. RFC 8555 for ACME. W3C performance timing specifications for RUM. SRE material for SLOs and error budgets.