Anycast DNS, Routing, and Load Balancing Clearly Defined

TL;DR

Anycast DNS determines which IP address a client receives for a service. However, it does not distribute individual TCP connections or HTTP requests. These tasks begin only after DNS resolution: Anycast Routing directs traffic to an edge location, Layer 4 distributes connections, and Layer 7 evaluates HTTP requests. This separation is the foundation of a resilient edge architecture.

Introduction

The assumption that Anycast DNS automatically distributes every connection or HTTP request to the optimal backend leads to incorrect architectural decisions. DNS operates before the actual connection establishment and provides responses that are cached by recursive resolvers and clients. Afterward, IP routing decides which edge location the packets reach. Only there can Layer 4 or Layer 7 components distribute connections and requests to backends. Thus, Anycast DNS, Anycast Routing, and Load Balancing operate at different levels. Mixing these levels overestimates the control capabilities of DNS and underestimates the importance of the public entry point before the applications.

1. Anycast DNS Determines the Reachable Target Address

Anycast DNS provides the same service across multiple geographically and network-distributed DNS locations. For a DNS query, there is not necessarily only a single authoritative server as the target. Internet routing directs the query to a reachable location that provides a DNS response. This response typically contains one or more IP addresses for the requested service.

Thus, the task of Anycast DNS ends here. DNS determines which address a client should use, not which backend processes a single HTTP request. Additionally, the authoritative DNS infrastructure does not reliably control the timing of each subsequent connection: resolvers and operating systems use caches according to DNS parameters. Therefore, a change in the response does not immediately affect all clients.

In the ayedo Edge Cloud, Anycast DNS, along with Multi-Provider DNS, is part of the platform’s public accessibility. This creates redundancy at the DNS level but does not replace the routing of subsequent traffic or the load balancing before the applications.

2. Anycast Routing Directs Packets to the Edge

After DNS resolution, the client establishes a connection to the returned IP address. At this point, DNS no longer applies, but IP routing does. With Anycast, multiple edge locations can announce the same IP address. Routers on the internet choose a reachable path to one of these locations based on their routing decision. This selection is influenced by topology and network, not the result of evaluating each individual HTTP request.

Anycast Routing can direct traffic to another edge location in the event of failures or changes in reachability. However, it does not guarantee that all packets of an application session take the same path worldwide or that the geographically nearest location is selected. Routing follows available paths and their preferences. Therefore, for the stability of higher protocols, it remains crucial how the edge connections are processed.

The ayedo Edge Cloud utilizes its own network infrastructure, an autonomous system, and a distributed Multi-PoP architecture in an active-active principle. These features anchor the public entry network-wise before the backends. However, they are not equivalent to deciding which specific backend receives a connection or request.

3. Layer 4 Distributes Connections, Layer 7 Understands Requests

When a connection reaches the edge, the tasks of load balancing begin. Layer-4 load balancing operates at the transport level, for example, with TCP or UDP. It can distribute incoming connections to available backends without needing to analyze the content of an HTTP request. This is relevant for protocols and services that do not rely on HTTP or where a transport decision suffices.

Layer-7 load balancing, on the other hand, operates at the application level. For HTTP or HTTPS, attributes such as hostname, path, or headers can influence routing decisions. For this, the edge must understand the application traffic; with HTTPS, TLS termination at the edge is often required. Layer 7 thus offers more control options but also increases complexity and responsibility for correct protocol processing.

The ayedo Edge Cloud supports Anycast-based Layer-4 and Layer-7 load balancing. Backend health checks and failover allow unavailable targets to be removed from distribution. Backend cloaking separates the public entry from directly reachable backend addresses. DNS thus provides the access point; the actual distribution of connections and requests occurs only within the edge.

4. The Levels Must Fit Together in the Architecture

The four levels perform different tasks: DNS publishes reachability, Anycast Routing directs packets to an edge location, Layer 4 processes transport connections, and Layer 7 evaluates application requests. This chain is not arbitrarily interchangeable. A low TTL value does not make DNS a request router, for example. Similarly, Layer-7 load balancing cannot make a decision if traffic does not reach the edge due to an upstream network problem.

For operations, this separation means that errors must be systematically isolated. A faulty DNS response, a routing problem, an unreachable edge location, and a failed backend produce different symptoms. Metrics and traffic statistics should therefore make the path from the DNS result to backend processing traceable.

This architecture is provider-independent. The ayedo Edge Cloud can connect ayedo Managed Kubernetes , its own Kubernetes clusters, or clusters with other providers as backends. This keeps the public entry with DNS, Anycast Routing, and load balancing separate from the choice of compute infrastructure.

Practical and Operational Scenario

A company operates an API in two Kubernetes clusters with different providers. The DNS name points to an Anycast address provided by the edge. A client queries this address via its resolver. The DNS response is cached; a single subsequent API request does not necessarily trigger a new DNS query.

During connection establishment, Anycast Routing directs the traffic to a reachable edge location. For TCP, Layer 4 can forward a connection to a healthy cluster. For HTTP, Layer 7 can additionally route based on the hostname or path. If a health check reports a backend failure, failover within the edge processing takes effect. DNS did not need to redistribute each individual request.

FAQ

Does Anycast DNS Distribute Individual HTTP Requests?

No. DNS provides addresses and is decoupled by caches. The distribution of individual connections or HTTP requests occurs only after connection establishment by Layer-4 or Layer-7 components.

Is Anycast Routing the Same as Load Balancing?

No. Anycast Routing selects a reachable network path to an edge location. Load balancing subsequently distributes connections or requests to backends.

When Is Layer-7 Load Balancing Required?

When routing decisions depend on the HTTP context, such as hostname or path. For pure transport distribution or non-HTTP services, Layer 4 may be sufficient.

Conclusion

Anycast DNS, Anycast Routing, and Load Balancing form a sequence, but they are not synonyms. DNS decides on the published target address, internet routing on the reachable edge path, and Layer 4 or Layer 7 on the processing of traffic. For companies, this distinction is relevant because it precisely assigns failover, observability, and operational responsibility. The ayedo Edge Cloud connects these levels before applications and APIs without architecturally mixing them.