VG ALB

resources map

routing

Great question 👌 — let’s break this down step by step.

---

🔹 1. Condition vs Routing Rule

• Condition → The “IF” part. What must match before ALB takes action. Example:

  • Host header = example.com

  • Path = /api/*

  • HTTP header contains X-Env=prod

• Routing Rule (Action) → The “THEN” part. What ALB should do if the condition matches. Example:

  • Forward traffic to Target Group A

  • Redirect to another URL

  • Return a fixed response

👉 Together: If condition is met → Apply routing rule (action).

---

🔹 2. Your Example: One domain (example.com), 3 services on same server

Suppose you have:

• Service A → running on port 8081

• Service B → running on port 8082

• Service C → running on port 8083

All are on the same EC2 instance (same private IP).

You can configure 3 Target Groups, each pointing to the same instance but different port:

• tg-service-a → 10.0.1.5:8081

• tg-service-b → 10.0.1.5:8082

• tg-service-c → 10.0.1.5:8083

Then ALB Listener rules:

• If Path = /service-a/* → forward to tg-service-a

• If Path = /service-b/* → forward to tg-service-b

• If Path = /service-c/* → forward to tg-service-c

---

🔹 3. Example Rule Setup (in words)

• Condition: Host header = example.com AND Path = /service-a/*

  • Action: Forward to Target Group A (port 8081)

• Condition: Host header = example.com AND Path = /service-b/*

  • Action: Forward to Target Group B (port 8082)

• Condition: Host header = example.com AND Path = /service-c/*

  • Action: Forward to Target Group C (port 8083)

---

🔹 4. Request Flow

1. User hits https://example.com/service-a/orders

2. ALB Listener checks Host = example.com → ✅ match

3. Path = /service-a/* → ✅ match

4. ALB forwards to tg-service-a → instance:8081

5. Service A responds → back through ALB → to user.

---

✅ So in short:

• Conditions = "when should I trigger this rule?"

• Routing Rules (Actions) = "what should I do when condition is met?"

---

⚡ Question for you: In your setup, do you want all 3 services under one domain with different paths (/service-a, /service-b, /service-c), or under different subdomains (a.example.com, b.example.com, c.example.com)?

The ALB config changes slightly depending on this.

target type: instance - can send across mulitple port or instances

targte type: ip - farget/ecs - to multiple ip like ecs tasks ip

one load balancer - added in cname of cloudflare records and handling traffic

like when host header matches eg. apierpr02.officevg.com then route traffic to target