Ambassador pattern in Microservices - Architecture Diagram

System Overview - Ambassador pattern

The Ambassador pattern is used in microservices to add a helper component (the ambassador) alongside a service. This helper manages communication tasks like logging, monitoring, or security, so the main service can focus on its core work. It helps keep services simple and reusable while handling cross-cutting concerns.

Architecture Diagram

User
  |
  v
+-----------------+
| Load Balancer   |
+-----------------+
        |
        v
+-----------------+       +-------------------+
| Ambassador      |<----->| External Service  |
| (Sidecar Proxy) |       +-------------------+
+-----------------+
        |
        v
+-----------------+
| Main Service    |
+-----------------+
        |
        v
+-----------------+
| Database        |
+-----------------+

Components

User

client

Initiates requests to the system

Load Balancer

load_balancer

Distributes incoming requests evenly to ambassador instances

Ambassador (Sidecar Proxy)

service_proxy

Handles communication tasks like retries, logging, and security for the main service

Main Service

service

Processes core business logic

External Service

external_service

Third-party or external system the ambassador communicates with

Database

database

Stores persistent data for the main service

Request Flow - 8 Hops

User → Load Balancer

Load Balancer → Ambassador (Sidecar Proxy)

Ambassador (Sidecar Proxy) → External Service

Ambassador (Sidecar Proxy) → Main Service

Main Service → Database

Main Service → Ambassador (Sidecar Proxy)

Ambassador (Sidecar Proxy) → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Ambassador (Sidecar Proxy)

Impact:Communication tasks like retries, logging, and security fail, causing possible request failures or security issues. Main service may receive unfiltered or unauthorized requests.

Mitigation:Deploy multiple ambassador instances with health checks and automatic restarts. Use circuit breakers and fallback mechanisms in main service to handle ambassador failures gracefully.

Architecture Quiz - 3 Questions

What is the main purpose of the Ambassador in this pattern?

A To store persistent data for the service

B To handle communication tasks like retries and security for the main service

C To balance load between users

D To replace the main service logic

Design Principle

The Ambassador pattern separates communication concerns from the main service by using a sidecar proxy. This keeps the service focused on business logic while the ambassador handles retries, logging, and security. It improves modularity, reusability, and simplifies service code.

Practice

1. What is the main purpose of the Ambassador pattern in microservices architecture?

easy

A. To directly expose services to the internet without any proxy

B. To replace the main service with a new version

C. To store data in a centralized database

D. To add a helper component that manages communication between services

Solution

1. Step 1: Understand the role of the Ambassador pattern

   The Ambassador pattern introduces a helper component that acts as a proxy or sidecar to handle communication tasks for a service.

2. Step 2: Compare options with the pattern's purpose

   Replacing services, storing data centrally, or exposing services directly do not describe the Ambassador pattern's role.

3. Final Answer:

   To add a helper component that manages communication between services -> Option D

4. Quick Check:

   Ambassador pattern = helper component for communication [OK]

Hint: Ambassador adds a helper proxy for communication [OK]

Common Mistakes:

• Confusing Ambassador with database or service replacement
• Thinking it exposes services directly without proxy
• Assuming it stores data centrally

2. Which of the following is the correct way to describe the Ambassador pattern's deployment style?

easy

A. A sidecar proxy deployed alongside the main service

B. A centralized database for service communication

C. A standalone service that replaces the main service

D. A load balancer that distributes traffic among services

Solution

1. Step 1: Identify deployment style of Ambassador pattern

   The Ambassador pattern is typically deployed as a sidecar proxy next to the main service to handle communication.

2. Step 2: Eliminate incorrect deployment types

   It is not a standalone replacement, centralized database, or load balancer.

3. Final Answer:

   A sidecar proxy deployed alongside the main service -> Option A

4. Quick Check:

   Ambassador deployment = sidecar proxy [OK]

Hint: Ambassador runs as a sidecar proxy next to service [OK]

Common Mistakes:

• Thinking Ambassador replaces the main service
• Confusing it with load balancer or database
• Assuming it is a standalone service

3. Consider this simplified pseudo-code for an Ambassador proxy handling requests:

class AmbassadorProxy {
  sendRequest(request) {
    if (this.isServiceAvailable()) {
      return this.forward(request);
    } else {
      return this.retry(request);
    }
  }
}

What will happen if the main service is temporarily down?

medium

A. The proxy forwards the request without checking availability

B. The proxy retries sending the request until the service is available

C. The proxy immediately returns an error without retrying

D. The proxy stores the request permanently without forwarding

Solution

1. Step 1: Analyze the sendRequest method logic

   The method checks if the service is available. If yes, it forwards the request; otherwise, it retries.

2. Step 2: Determine behavior when service is down

   If the service is down, isServiceAvailable() returns false, so retry(request) is called to resend the request.

3. Final Answer:

   The proxy retries sending the request until the service is available -> Option B

4. Quick Check:

   Service down triggers retry in Ambassador proxy [OK]

Hint: Ambassador retries requests if service unavailable [OK]

Common Mistakes:

• Assuming proxy forwards without checking
• Thinking proxy returns error immediately
• Believing proxy stores requests permanently

4. A developer wrote this Ambassador proxy code snippet:

class Ambassador {
  send(request) {
    if (this.checkService()) {
      this.forward(request);
    } else {
      this.retry(request);
    }
  }
}

But requests are never retried even when the service is down. What is the likely bug?

medium

A. The send method does not return the result of retry or forward

B. The method forward does not return the response

C. The checkService method always returns true

D. The retry method is not implemented

Solution

1. Step 1: Review send method behavior

   The send method calls forward or retry but does not return their results, so caller never sees retries.

2. Step 2: Understand impact on retry behavior

   Without returning retry's result, retries may happen but caller ignores them, appearing as if no retry occurs.

3. Final Answer:

   The send method does not return the result of retry or forward -> Option A

4. Quick Check:

   Missing return in send causes retry to be ignored [OK]

Hint: Always return retry/forward results in proxy methods [OK]

Common Mistakes:

• Assuming checkService always true without checking
• Thinking retry method is missing
• Ignoring return values in send method

5. You want to improve observability and security for a microservice without changing its code. How does the Ambassador pattern help achieve this?

hard

A. By replacing the microservice with a new secure version

B. By modifying the service code to include security and logging libraries

C. By adding a sidecar proxy that handles logging, retries, and TLS encryption transparently

D. By deploying a centralized monitoring service that polls the microservice directly

Solution

1. Step 1: Identify how Ambassador pattern enhances observability and security

   The Ambassador pattern uses a sidecar proxy to add features like logging, retries, and TLS without changing the main service code.

2. Step 2: Compare with other options

   Modifying service code, polling directly, or replacing service do not align with Ambassador pattern benefits.

3. Final Answer:

   By adding a sidecar proxy that handles logging, retries, and TLS encryption transparently -> Option C

4. Quick Check:

   Ambassador adds security and observability via sidecar proxy [OK]

Hint: Ambassador adds features without changing service code [OK]

Common Mistakes:

• Thinking service code must be changed
• Confusing Ambassador with centralized monitoring
• Assuming service replacement is needed