[Solved] An ALB has two target groups: tgA and tgB. A listener rule forwards requests with host header app.example.... What happens when a request arrives with host header api.example.com? | AWS

AWS - Elastic Load Balancing

An ALB has two target groups: tgA and tgB. A listener rule forwards requests with host header app.example.com to tgA and all other hosts to tgB. What happens when a request arrives with host header api.example.com?

AThe ALB returns a 404 error because the host header does not match.

BThe request is routed to target group <code>tgA</code>.

CThe request is routed to target group <code>tgB</code>.

DThe ALB forwards the request to both <code>tgA</code> and <code>tgB</code> simultaneously.

Step-by-Step Solution

Solution:

Step 1: Understand the listener rule
The ALB listener rule routes requests with host header app.example.com to tgA.
Step 2: Analyze the incoming request
The request has host header api.example.com, which does not match app.example.com.
Step 3: Determine routing behavior
Since the host header does not match the rule, the ALB routes the request to the default target group, which is tgB.
Final Answer:
The request is routed to target group tgB. -> Option C
Quick Check:
Host header matching routes to specified target group; unmatched goes to default [OK]

Quick Trick: Host header rules route matching hosts; others go default [OK]

Common Mistakes:

Assuming unmatched hosts cause errors
Thinking ALB forwards to multiple target groups simultaneously
Confusing host header with path-based routing

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What happens when a request arrives with host header api.example.com?

Step 1: Understand the listener rule

Step 2: Analyze the incoming request

Step 3: Determine routing behavior

Final Answer:

Quick Check:

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