Listener rules and routing in AWS - Step-by-Step Execution

Process Flow - Listener rules and routing

Client sends request

↓

Listener receives request

↓

Evaluate listener rules in order

↓

Match rule condition?

No→Check next rule

Yes↓

Route request to target group

↓

Target group forwards to registered targets

↓

Response sent back to client

Requests come to a listener, which checks rules one by one. When a rule matches, it routes the request to a target group that sends it to servers.

Execution Sample

AWS

Listener rules:
1) If path is /images/* -> TargetGroupImages
2) If host is example.com -> TargetGroupMain
Default -> TargetGroupDefault

Routes requests based on path or host to different target groups.

Process Table

Step	Request Detail	Rule Evaluated	Condition Result	Action Taken	Routing Outcome
1	Host: example.com, Path: /images/cat.jpg	Rule 1: Path /images/*	Match	Route to TargetGroupImages	Request sent to TargetGroupImages
2	Host: example.com, Path: /home	Rule 1: Path /images/*	No Match	Check next rule	No routing yet
3	Host: example.com, Path: /home	Rule 2: Host example.com	Match	Route to TargetGroupMain	Request sent to TargetGroupMain
4	Host: unknown.com, Path: /about	Rule 1: Path /images/*	No Match	Check next rule	No routing yet
5	Host: unknown.com, Path: /about	Rule 2: Host example.com	No Match	Check next rule	No routing yet
6	Host: unknown.com, Path: /about	Default rule	Always Match	Route to TargetGroupDefault	Request sent to TargetGroupDefault

💡 Routing stops when a rule matches or default rule is applied.

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 6
Request Host	example.com	example.com	example.com	unknown.com
Request Path	/images/cat.jpg	/images/cat.jpg	/home	/about
Current Rule	None	Rule 1	Rule 2	Default rule
Routing TargetGroup	None	TargetGroupImages	TargetGroupMain	TargetGroupDefault

Key Moments - 3 Insights

Why does the listener check rules in order and stop at the first match?

Listener rules are evaluated top to bottom. Once a rule matches, routing happens immediately (see execution_table rows 1 and 3). This prevents multiple routes for one request.

What happens if no rules match the request?

If no specific rule matches, the default rule routes the request (see execution_table row 6). This ensures every request is handled.

Can multiple rules match the same request?

Yes, but only the first matching rule is used for routing (see execution_table rows 1 and 3). Later matches are ignored.

Visual Quiz - 3 Questions

Look at the execution table, which target group handles the request with Host: example.com and Path: /home?

A TargetGroupImages

B TargetGroupMain

C TargetGroupDefault

D No routing

💡 Hint

Check execution_table row 3 where the host matches example.com and path is /home.

At which step does the listener apply the default rule?

A Step 6

B Step 4

C Step 5

D Step 3

💡 Hint

Look for the row where the default rule is applied in execution_table.

If the first rule was removed, where would the request with path /images/cat.jpg be routed?

A TargetGroupDefault

B TargetGroupImages

C TargetGroupMain

D No routing

💡 Hint

Without rule 1, the listener checks rule 2 next; see execution_table logic.

Concept Snapshot

Listener rules check incoming requests in order.
Each rule has a condition (like path or host).
First matching rule routes to a target group.
If none match, default rule routes request.
Rules prevent multiple routes for one request.

Full Transcript

When a client sends a request, the listener receives it and evaluates rules one by one. Each rule has a condition such as matching the request path or host. The listener checks the first rule; if it matches, it routes the request to the specified target group and stops checking further rules. If it does not match, it moves to the next rule. If no rules match, the default rule routes the request to a default target group. This process ensures every request is routed correctly and only once.