Context and Problem
Modern cloud applications often need to connect to external services or resources that:
- Each service implements its own connection handling, retry logic, and error handling
- Have complex connection requirements
- Require client-side resiliency patterns (retry, circuit breaking)
- May change configuration or endpoints over time
- Need monitoring, logging, or security handling for outbound connections
- Require different implementations across various programming languages or frameworks
Solution
The Ambassador pattern creates a helper service that acts as an out-of-process proxy:
- Co-located with the client service (same host, container, or pod)
- Handles common client connectivity tasks
- Provides a simplified local interface to the client
- Manages cross-cutting concerns like circuit breaking, routing, metering, and monitoring
- Insulates the client from direct interaction with external dependencies
Benefits
- Separation of concerns
- Client code only handles business logic, while connectivity concerns are managed separately
- Consistency
- Implements connectivity patterns uniformly across different services
- Reusability
- Allows sharing of client libraries across applications with different technology stacks
- Simplified testing
- Makes mocking external dependencies easier
- Enhanced observability
- Centralizes logging and monitoring of external communications
- Reduced client complexity
- Offloads circuit breaking, retries, and other resiliency patterns
Trade-offs
- Additional latency
- Introduces an extra hop in the request path
- Increased deployment complexity
- Requires deploying and managing the ambassador alongside each service
- Resource overhead
- Consumes additional memory and CPU compared to in-process libraries
- Potential single point of failure
- If not implemented properly, ambassador failures can affect the entire client
Issues and Considerations
- Deployment coupling
- The ambassador must be deployed alongside the client service
- Configuration management
- How to synchronize configuration between client and ambassador
- Performance impact
- Assess the performance overhead for your specific scenario
- Protocol support
- Ensure the ambassador supports all required communication protocols
- Error handling
- Define how errors are propagated back to the client service
- Versioning
- Manage updates to the ambassador without disrupting client services
When to Use This Pattern
- You need consistent client-side resiliency patterns across multiple services
- You're working in polyglot environments with multiple programming languages
- External service connection details change frequently
- You need to offload cross-cutting connection logic from application code
- You want centralized monitoring of outbound service calls
- Client services need insulation from changes to external service implementations