Global Traffic Management
Global traffic management decides which healthy application location should receive a user’s connection. It combines traffic-steering policy, health signals, and global delivery mechanisms such as DNS, anycast, and proxies.
itWeb servers, proxies, and traffic management | OpenSkills.info
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Intro
Global Traffic Management
An application can run in several regions and still fail its users. A healthy region may be far away. A failed region may remain in cached DNS answers. A health check may test the wrong path. A sudden failover may send more traffic than the surviving region can handle.
Global traffic management addresses these problems. It selects an application location for each user or resolver. The selection can reflect availability, latency, geography, capacity, rollout policy, or a fixed priority.
The key idea is separation. A traffic manager makes a placement decision. The selected location still needs a local load balancer, healthy application instances, sufficient capacity, and consistent data.
The control loop
A useful mental model has five stages:
- Observe endpoint health and performance from relevant locations.
- Evaluate a policy against the eligible locations.
- Publish or enforce a traffic decision.
- Observe the result from the user’s path.
- Adjust the policy or endpoint set when evidence changes.
The loop is only as good as its signals. A TCP connection proves that a port accepted a connection. An HTTP check can test a path and expected response. Neither test automatically proves that every dependency or user journey works.
Three steering planes
DNS steering
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Sources
- https://www.rfc-editor.org/rfc/rfc9499.html
Supports
- Authoritative server and recursive resolver roles
- DNS caching, record sets, and TTL terminology
- Separation between DNS resolution and later application connections
- https://www.rfc-editor.org/rfc/rfc4786.html
Supports
- Anycast service addresses, nodes, catchments, and route-based selection
- Coarse and potentially uneven load distribution
- Location-dependent monitoring and routing changes
- Transaction duration, node autonomy, and data synchronization limits
- https://www.rfc-editor.org/rfc/rfc8767.html
Supports
- Resolver use of stale cached data when authoritative refresh fails
- TTL as the duration before the source must again be consulted
- Resiliency and freshness tradeoffs during DNS failure
- https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-policy.html
Supports
- Failover, weighted, latency, geolocation, geoproximity, IP-based, and multivalue DNS policies
- Different policies serving different placement intents
- https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/route-53-concepts.html
Supports
- Recursive resolver reuse of cached values before TTL expiry
- TTL expressed as a DNS cache duration
- https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/dns-failover.html
Supports
- Endpoint, calculated, and alarm-based health checks
- DNS failover from an unhealthy resource to a healthy resource
- https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/dns-failover-simple-configs.html
Supports
- Health checks running periodically rather than in response to each DNS query
- Routing-policy selection combined with record health
- https://developers.cloudflare.com/load-balancing/monitors/
Supports
- Regular health probes, endpoint status, and pool removal
- Multi-region health vantage points and majority evaluation
- HTTP, HTTPS, TCP, and other monitor behavior
- https://developers.cloudflare.com/reference-architecture/architectures/load-balancing/
Supports
- Priority, weighted, geographic, dynamic, proximity, and request-aware steering
- Endpoint pools, health thresholds, and probe path design
- DNS and layer seven proxy traffic management distinctions
- Active destination selection and fallback behavior
- https://developers.cloudflare.com/load-balancing/load-balancers/common-configurations/
Supports
- Active-passive and active-active pool arrangements
- Failure thresholds, fallback pools, and traffic transfer
- https://developers.cloudflare.com/load-balancing/reference/load-balancing-analytics/
Supports
- Traffic flow, endpoint health, and pool health analysis
- Filtering by pools, regions, and endpoints
- https://github.com/sindresorhus/awesome
Supports
- Discovery of the Awesome SDN list from the canonical awesome index
- https://github.com/sdnds-tw/awesome-sdn
Supports
- Discovery of FRRouting and BIRD as BGP routing projects
- https://docs.frrouting.org/en/latest/
Supports
- FRRouting as an IP routing suite with BGP
- User guidance for routing policy, route state, configuration, and operations
- https://bird.network.cz/doc/bird.html
Supports
- BIRD user documentation for BGP, routing tables, filters, and diagnostics
