SOA-C02 Networking and Content Delivery Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  The ALB's health check interval is too short, causing instances to be marked unhealthy

  Why it's wrong here

  The ALB health check interval determines how frequently the load balancer sends requests to an instance to assess its status, but it has no effect on the persistence of client sessions. A shorter interval merely increases probe frequency; as long as the instance continues to return healthy responses, it remains eligible to receive traffic and its existing stickiness cookies remain valid. Session loss here is caused by the application-side session expiring before the ALB's stickiness duration, not by any health check misconfiguration.

• ✗

  The application cookie is overwriting the ALB's stickiness cookie

  Why it's wrong here

  The ALB's stickiness feature uses a dedicated, load-balancer-generated cookie (typically named AWSALB) that is encrypted and stored separately from any application cookies. An application cookie, such as a session identifier, cannot overwrite or corrupt the ALB's stickiness cookie because they use different names and are written by different layers. Even if an application attempts to set a cookie with the same name, the ALB overwrites it with its own value on the response, ensuring that the routing persistence remains intact. Therefore, cookie interference is not a plausible cause of lost sessions.

• ✗

  Cross-zone load balancing is disabled on the ALB

  Why it's wrong here

  Cross-zone load balancing controls whether an ALB node can distribute traffic to targets located in other Availability Zones; when disabled, each node only receives traffic from its own zone and routes to targets in that same zone. This setting affects the distribution of load across AZs but does not alter how the ALB uses its stickiness cookie to route a client to the same target instance. A client's session will still be pinned to the same instance as long as the cookie is valid, regardless of the cross-zone setting. Thus, this misconfiguration cannot explain why sessions are lost.

• ✓

  The application's session cookie has a shorter expiration than the ALB's stickiness duration

  Why this is correct

  In this scenario, the ALB's stickiness cookie (AWSALB) remains valid and continues to route the client to the same EC2 instance for the configured duration, but the application's own session cookie (e.g., JSESSIONID) expires earlier. Once the application session expires, the server-side session data is discarded or considered invalid, causing the user to be logged out even though the ALB still sends them to the exact same server. The user then perceives a lost session, but the underlying issue is the mismatch between the application session timeout and the ALB stickiness duration, not the load balancer's routing behavior.

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