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Choose an Application Load Balancer (ALB) when routing must inspect HTTP requests—for example, to send different hosts or URL paths to different services. Choose a Network Load Balancer (NLB) when the design needs network-level traffic handling, static addresses for enabled Availability Zones, or protocols such as TCP, UDP, or TLS. If you need both a fixed or PrivateLink-capable entry point and HTTP-aware routing, AWS supports placing an NLB in front of an ALB, subject to topology constraints.
ALB vs. NLB: what is the practical difference?
The central distinction is what the load balancer can use to make a routing decision. An ALB operates at the application layer (OSI layer 7) and evaluates HTTP request details against listener rules. An NLB handles network traffic through listeners and target groups, and can provide static addresses per enabled Availability Zone. Neither is universally better: the appropriate choice depends on protocols, routing, addressability, and how targets are distributed across zones.
| Decision | ALB | NLB |
|---|---|---|
| Routing model | Layer-7 rules can inspect HTTP request content. | Network traffic handling through configured listeners and target groups. |
| Typical routing criteria or protocols | Host, path, headers, methods, query parameters, and source IP conditions. | Listener protocols include TCP, TLS, UDP, and TCP_UDP, subject to the selected configuration. |
| Addressing | DNS-based addresses; documented address types include IPv4 and dual-stack options. | Static IP address per enabled zone; internet-facing NLBs can use an Elastic IP per zone. |
| Cross-zone default | Enabled at the load-balancer level; a target group can opt out. | Disabled by default; can be enabled. |
| Combining capabilities | Can provide HTTP-aware routing behind an NLB. | Can provide the entry point in front of an ALB. |
These capability differences are documented by AWS for ALB and AWS for NLB. Exact feature support can depend on listener protocol, target-group settings, target type, and address family.
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Use an ALB when application requests need different destinations or actions based on their content. Its listener rules are evaluated by priority; when a rule’s conditions match, the ALB performs its configured action and selects a target from the associated target group.
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ALB fits request-aware web routing
- Route different hostnames or URL paths to separate applications or services.
- Use supported request conditions involving headers, HTTP methods, query parameters, or source IP addresses.
- Configure actions such as redirects or custom responses alongside forwarding rules.
ALB targets can include EC2 instances, containers, and IP addresses. Health checks are configured at the target-group level. AWS also documents HTTP/2 on HTTPS listeners and WebSocket upgrades in its load-balancer behavior guide; check the current documentation for the particular listener and feature you plan to use.
When should you use an NLB?
Use an NLB when the entry point needs network-level traffic handling or stable per-zone addresses, or when the application requires a supported listener protocol beyond HTTP request routing. NLB distributes traffic to registered targets in one or more Availability Zones. AWS documents support for connections through VPC peering, AWS managed VPN, Direct Connect, and third-party VPN solutions.
NLB fits fixed-address and network-protocol requirements
- Use its static IP address for each enabled Availability Zone when clients or network controls require stable addresses.
- For an internet-facing NLB, associate an Elastic IP per zone when that is part of the design.
- Assess TCP, TLS, UDP, or TCP_UDP listeners for the required traffic, then verify the compatible target-group protocol and address-family configuration.
Address and protocol behavior is configuration-dependent. Consult the current NLB documentation before settling on a listener and target-group combination.
How does cross-zone load balancing affect the design?
With cross-zone load balancing enabled, a load-balancer node can distribute traffic across targets in all enabled Availability Zones. When it is off, each node sends traffic only to targets in its own zone. The default differs: ALB has cross-zone balancing enabled at the load-balancer level, though a target group can explicitly disable it; NLB has it disabled by default.
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That difference matters when target counts or traffic are uneven across zones. With cross-zone disabled, each zone’s local target capacity must be considered against traffic arriving there. Do not assume disabling it will always reduce cost or latency; the result depends on topology and traffic. For ALB target groups, AWS says target stickiness is not supported when cross-zone balancing is off, and Lambda targets are not supported in that mode. See AWS cross-zone load-balancing documentation and the relevant ALB target-group settings.
Can you put an NLB in front of an ALB?
Yes. AWS supports registering an ALB as a target in an NLB target group. This arrangement can combine NLB entry-point capabilities, such as static IP addresses or PrivateLink endpoint services, with ALB layer-7 request routing. AWS also describes it for applications using one endpoint for multiple protocols, such as media services that use HTTP for signaling and RTP for streaming.
Topology constraints to account for
- A target group can register one ALB.
- The NLB and ALB must be in the same VPC and AWS account.
- An ALB can be registered with up to two NLBs through separate target groups.
- Communication from the NLB to the ALB uses IPv4.
- Registering an ALB reduces the maximum number of targets per Availability Zone per NLB by 50.
These constraints are described in AWS guidance on using an ALB as an NLB target. Confirm current quotas and configuration details before production deployment.
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How to choose for a new deployment
- List client-facing protocols. Identify whether traffic is HTTP-aware or includes network protocols such as TCP, TLS, or UDP-family traffic. If routing depends on HTTP request fields, assess ALB first.
- Check address requirements. Determine whether clients need stable per-zone IP addresses or an internet-facing Elastic IP per zone; if so, assess NLB.
- Decide whether a combined design is justified. Put NLB in front of ALB only when the entry point needs NLB characteristics while the application still needs ALB request routing.
- Plan Availability Zones and targets together. Choose enabled zones and register targets in them. Evaluate cross-zone behavior against target counts, zonal resilience goals, and expected traffic.
- Validate the final configuration. Check listener and target-group protocols, address family, health checks, security-group rules, service quotas, and current AWS pricing for the exact region and design.
What this comparison does not establish
There is no universal performance winner established here, and the available information does not establish a price winner. Workload-specific performance depends on the design and traffic, while pricing depends on region, usage, and selected features. Compare current AWS pricing and test the actual workload before making a cost or performance decision.
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