AWS Advanced Networking Specialty<\/a>, but its design principles apply to every hybrid network carrying important application or data flows. The questions start with what may fail, how rapidly routing should adapt, and what happens when a connection is available but unhealthy.<\/p>\nStart from the workload’s connectivity objective<\/h3>\n
Not every application requires the same network availability. A nightly analytics export can tolerate a delayed transfer; a point-of-sale authorization system may have a short recovery-time objective and a strict limit on transaction interruption. Map each critical flow, dependency, and tolerance before selecting a Direct Connect resiliency model. An SLA objective is not a complete description of what users will experience during failover.<\/p>\n
Distinguish network availability from application continuity. A route can recover while a stateful session still fails, or the application may continue processing because it has buffered messages locally. Conversely, a perfectly healthy circuit cannot repair a database or identity provider outage. Business tests should measure end-to-end behavior during the actual failover path, not merely whether the BGP session eventually reestablishes.<\/p>\n
List the dependencies explicitly: customer premises equipment, power, cross-connects, partner facilities, last-mile carriers, Direct Connect locations, AWS regions, virtual interfaces, gateways, and routing policy. Where two paths share an item, determine whether that item can fail both at once. A design review that asks only for two circuit IDs will miss the larger part of the risk.<\/p>\n
Understand the AWS resiliency models<\/h3>\n
AWS’s Direct Connect Resiliency Toolkit offers models with different redundancy targets. The maximum-resiliency model is intended to support the requirements for a 99.99 percent Direct Connect SLA; the high-resiliency model targets the requirements for a 99.9 percent SLA; and a development-and-test model provides more limited redundancy for noncritical systems. Achieving the stated SLA depends on meeting the full applicable service-level conditions, not simply selecting a model in a wizard.<\/p>\n
Maximum resiliency uses separate Direct Connect locations and redundant connections arranged to avoid single-device or single-location dependence. High resiliency still incorporates important redundancy but has a different failure-tolerance target. A development environment may justify separate devices in one location because its business consequence is much smaller. These are design patterns with different costs and assumptions, not badges that automatically certify application uptime.<\/p>\n
Ordering and deployment must reflect physical reality. Partner-provided connectivity may introduce additional shared carrier infrastructure outside the AWS console. Request path diversity details from providers and confirm that documented redundancy corresponds to actual circuits. A diagram showing two geographically separate AWS locations is incomplete if both customer-side paths leave the building through one conduit.<\/p>\n
Understand BGP failover and route selection<\/h3>\n
Border Gateway Protocol exchanges reachable prefixes across Direct Connect virtual interfaces. Advertisements and policies determine which paths traffic prefers under healthy conditions and which alternatives become eligible when a path disappears. A backup circuit that is technically active but never selected because of conflicting routing preferences does not deliver the expected behavior. Equally, unexpected route preference can move traffic to a distant or expensive path during normal operation.<\/p>\n
Route design must be reviewed in both directions. Customer-to-AWS traffic may prefer one connection while return traffic follows a different path. This asymmetry can be acceptable in some architectures but problematic for stateful inspection, troubleshooting, or appliances with path expectations. Engineers should document AWS-side and customer-side route decisions, advertised prefixes, aggregation, and the expected behavior when an individual BGP session fails.<\/p>\n
Do not treat BGP convergence time as the sole measure of recovery. An application using persistent transport sessions may need to reconnect. DNS and endpoint choices can shape regional alternatives. Firewalls must allow the replacement path. Packet loss may degrade service without fully dropping BGP. Health checks, telemetry, and operational procedures should therefore capture brownouts as well as clean disconnections.<\/p>\n
Separate connection, location, and region failures<\/h3>\n
A failed physical circuit is only one scenario. A cross-connect could be damaged, a provider may lose a backbone path, a Direct Connect location might become unavailable, or an AWS region might experience disruption affecting the application’s endpoints. Each scenario has a different recovery requirement. Designing only for a single-port failure can leave a business-critical system exposed to the first incident outside that assumption.<\/p>\n
Separate Direct Connect locations can reduce location concentration, but they do not automatically make the application multi-region. If a service is deployed solely in one region, network diversity cannot keep it running after a region-wide application failure. Regional continuity requires compatible compute, data replication, identity, endpoints, and failover ownership. Infrastructure resilience should be tested as an end-to-end property spanning networking and the workloads it serves.<\/p>\n
Public internet VPN can serve as a supplementary backup path where appropriate, but it has different performance, encryption, routing, and availability characteristics. Encrypt traffic as required by the data and risk model; a private path is not automatically an encrypted end-to-end one. Decide whether VPN is a viable safety net for selected critical prefixes or merely an emergency route for low-volume administrative access.<\/p>\n
Design the gateway and prefix boundaries<\/h3>\n
Direct Connect gateways and virtual interfaces provide connectivity options that determine which networks can communicate across locations and regions. Engineers need to understand which resources and attachments are involved, what prefixes are allowed, and how route propagation or manual filtering limits exposure. Allowing every corporate prefix into every environment may be expedient but often violates segmentation and produces confusing reachability.<\/p>\n
A typical enterprise has different treatment for payment systems, analytics networks, administrative services, and development. Each flow may need distinct inspection, bandwidth planning, and routing controls. Prefix lists and advertised routes should reflect these boundaries. More specific routes can unexpectedly override the intended aggregate fallback path; test the exact policy rather than relying on a generic ‘primary\/backup’ label.<\/p>\n
Capacity matters during failover. A secondary link that supports half the production demand will carry an outage into the application layer when the primary disappears. Model realistic peak traffic plus operational overhead, including bursty backups or data movement. Decide whether lower-priority transfers should be throttled during degraded operation so customer-facing traffic remains within service objectives.<\/p>\n
Test failover before an actual outage<\/h3>\n
Resiliency drills should isolate one failure at a time and then exercise combinations consistent with the threat model. Shut down a BGP peer in a controlled window, simulate a circuit loss, and validate return traffic, latency, application reconnection, and operational alerting. Repeat with the other path as primary. A backup connection that was tested once two years ago may no longer work after months of route and firewall changes.<\/p>\n
Observe more than ping. Check transactions, message delivery, authentication, session behavior, retransmissions, and recovery time. An application may recover a network route but need manual intervention to clear stale transport state. Record those requirements. If an outage requires an engineer to edit ten routes by hand, the nominal redundancy design has hidden dependence on human availability.<\/p>\n
A tabletop exercise complements technical tests. Ask who owns the AWS connection, who contacts the carrier, what constitutes an incident, how route changes are approved, and which evidence distinguishes provider loss from a customer-side firewall issue. Escalation paths can dominate recovery time even when the underlying BGP failover is straightforward. Keep contact information and diagnostic access usable when the normal corporate network is unavailable.<\/p>\n
Monitor independent paths and revisit the design<\/h3>\n
Collect circuit status, BGP session health, utilization, errors, and application latency for each path. Alert when redundancy has been lost even if traffic has not failed yet; a service running well on a single surviving connection is more vulnerable than the dashboard suggests. Pair network telemetry with a user-visible service indicator so engineers know when a degraded link is causing real business impact.<\/p>\n
Infrastructure changes can silently reintroduce shared failure points. Provider contract renewals, building moves, gateway changes, and network consolidations deserve a fresh diversity review. The resilience model that fit a pilot may be inadequate once workloads become revenue-critical. Cross-reference the broader AWS architecture design<\/a> so traffic distribution, region selection, and data dependencies support the same availability objective.<\/p>\nA financial institution should also understand the difference between planned and unplanned transitions. Maintenance on one Direct Connect location can be coordinated, traffic shifted deliberately, and staff placed on alert. An unplanned fiber cut offers no such preparation. Both conditions deserve testing, because scheduled maintenance alone often validates only the easiest transition. The backup path should handle sudden withdrawal of a route or loss of a carrier without requiring a privileged engineer to be awake and ready to improvise.<\/p>\n
Finally, review how recovery is communicated to application owners. Networking teams may declare success when traffic reaches a destination again, while business systems still have stale sessions or delayed transaction queues. A shared operational dashboard should show path state alongside transaction success, backlog recovery, and customer impact. That prevents premature incident closure and reveals whether nominally redundant infrastructure is adequate for the service-level promise.<\/p>\n
A reliable Direct Connect design is not ‘two links are present.’ It is a demonstrated ability to keep acceptable business operations running when a particular device, location, provider component, or route fails. Physical independence, correct routing, adequate backup capacity, and repeated end-to-end testing are what turn network redundancy into service resilience.<\/p>\n","protected":false},"excerpt":{"rendered":"
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