Envoy Review

ByObeydul Haque Reading Time: 7 minutes

Envoy is a Layer 7 (application layer) proxy designed to handle the networking needs of modern, distributed applications. It is often described as a “service mesh data plane” because of its integration with service mesh frameworks like Istio, Linkerd, and AWS App Mesh, but it can also function as a standalone proxy. Envoy is built to be highly performant, extensible, and observable, making it a go-to choice for organizations adopting microservices and cloud-native architectures.

Key features of Envoy include:

  • Dynamic configuration: Envoy supports hot-reloadable configurations via APIs, eliminating the need for service restarts.
  • Advanced load balancing: It offers sophisticated load balancing algorithms like round-robin, least request, and consistent hashing.
  • Observability: Built-in support for detailed metrics, logging, and distributed tracing.
  • Extensibility: A robust filter system allows custom logic to be injected into the request/response path.
  • Protocol support: Envoy supports HTTP/1.1, HTTP/2, HTTP/3, gRPC, WebSocket, TCP, and UDP, among others.

Envoy’s versatility makes it suitable for a variety of roles, including edge proxies, internal service proxies, and API gateways.

Architecture and Design

Core Concepts

Envoy’s architecture is modular and event-driven, built in C++ for performance. At its core, Envoy operates as a proxy that sits between services, intercepting and managing traffic. Its key architectural components include:

  • Listeners: These define how Envoy accepts incoming connections (e.g., on specific ports or IP addresses).
  • Filters: Filters process network traffic and can modify, observe, or route requests. Envoy supports filter chains for both HTTP and TCP traffic.
  • Clusters: A cluster is a group of upstream endpoints (services) that Envoy routes traffic to.
  • Routes: Routes define how requests are matched and forwarded to clusters based on headers, paths, or other criteria.
  • xDS APIs: Envoy’s dynamic configuration is powered by the xDiscovery Service (xDS) APIs, which allow real-time updates to listeners, clusters, routes, and more.

Data Plane vs. Control Plane

Envoy is a data plane component, meaning it handles the actual traffic routing and processing. It relies on a control plane (e.g., Istio, Consul, or a custom solution) to provide configuration and service discovery. This separation of concerns allows Envoy to remain lightweight and focused on performance while enabling flexibility in how it is managed.

Performance

Envoy’s C++ implementation ensures low latency and high throughput, even under heavy loads. Its event-driven, non-blocking I/O model allows it to handle thousands of concurrent connections efficiently. Benchmarks from the Envoy community show it can process millions of requests per second with sub-millisecond latency, making it ideal for high-traffic environments.

Key Features and Capabilities

1. Service Mesh Integration

Envoy is the default data plane for most service mesh implementations, including Istio, Linkerd, and AWS App Mesh. In a service mesh, Envoy runs as a sidecar proxy alongside each service instance, managing inter-service communication. This setup provides:

  • Traffic management: Fine-grained control over routing, retries, timeouts, and circuit breaking.
  • Security: Mutual TLS (mTLS) for encrypted communication and authentication.
  • Observability: Metrics and traces for monitoring service health and performance.

For example, Istio uses Envoy to enforce policies like rate limiting and A/B testing without requiring changes to application code.

2. Advanced Load Balancing

Envoy’s load balancing capabilities are a standout feature. It supports:

  • Weighted round-robin: Distributes traffic based on endpoint weights.
  • Least request: Routes traffic to the least busy upstream service.
  • Consistent hashing: Ensures sticky sessions for stateful applications.
  • Zone-aware routing: Prioritizes endpoints in the same availability zone to reduce latency.

These features are critical for large-scale systems where efficient resource utilization and fault tolerance are paramount.

3. Observability and Monitoring

Envoy’s observability features are among its strongest selling points. It generates detailed statistics (e.g., request rates, error codes, latency) and integrates with monitoring tools like Prometheus, Grafana, and Datadog. Distributed tracing is supported via integrations with Jaeger, Zipkin, and OpenTelemetry, allowing developers to trace requests across microservices.

For example, Envoy’s access logs provide granular details about each request, including headers, response codes, and timing. This level of visibility is invaluable for debugging and performance optimization.

4. Extensibility with Filters

Envoy’s filter system allows developers to extend its functionality. Filters can be written in C++, Lua, or WebAssembly (Wasm), enabling custom logic for tasks like:

  • Authentication and authorization
  • Request transformation (e.g., adding headers)
  • Rate limiting
  • Compression

The WebAssembly support, introduced in recent versions, has made it easier to write portable, secure filters without recompiling Envoy.

5. Protocol Support

Envoy’s protocol support is extensive, covering:

  • HTTP-based protocols: HTTP/1.1, HTTP/2, HTTP/3 (via QUIC), and gRPC.
  • WebSocket: For real-time, bidirectional communication.
  • TCP and UDP: For non-HTTP workloads like databases or messaging systems.

This versatility allows Envoy to handle diverse workloads, from web APIs to legacy systems.

6. Security Features

Envoy provides robust security features, including:

  • mTLS: Ensures encrypted, authenticated communication between services.
  • RBAC: Role-based access control for fine-grained authorization.
  • JWT authentication: Validates JSON Web Tokens for secure API access.

These features are particularly important in zero-trust environments, where all traffic must be verified.

Use Cases

Envoy’s flexibility makes it suitable for a wide range of use cases:

1. Edge Proxy

As an edge proxy, Envoy sits at the boundary of a system, handling external traffic. It can perform tasks like:

  • TLS termination
  • Rate limiting
  • Request routing to internal services

Companies like Lyft and Airbnb use Envoy as an edge proxy to manage ingress traffic.

2. Service Mesh Sidecar

In a service mesh, Envoy runs alongside each microservice, handling service-to-service communication. This is the most common use case, as it enables features like retries, circuit breaking, and observability without modifying application code.

3. API Gateway

Envoy can function as an API gateway, providing a unified entry point for APIs. It supports features like request transformation, authentication, and rate limiting, making it a lightweight alternative to dedicated API gateway solutions.

4. Legacy System Integration

For organizations with legacy systems, Envoy can act as a bridge between modern microservices and older monolithic applications. Its TCP proxying capabilities are particularly useful for this purpose.

5. Database Proxy

Envoy’s TCP and UDP support allows it to proxy database traffic, providing features like connection pooling and observability for databases like MySQL, PostgreSQL, and MongoDB.

Strengths of Envoy

  1. Performance: Envoy’s C++ implementation and event-driven architecture ensure low latency and high throughput.
  2. Flexibility: Its support for multiple protocols and use cases makes it a Swiss Army knife for networking.
  3. Ecosystem: Envoy’s integration with service meshes, monitoring tools, and cloud providers ensures it fits seamlessly into modern stacks.
  4. Community and Adoption: Backed by the Cloud Native Computing Foundation (CNCF), Envoy has a vibrant community and is used by industry leaders like Google, AWS, and Microsoft.
  5. Dynamic Configuration: The xDS APIs enable real-time updates, reducing downtime and operational complexity.

Limitations and Challenges

Despite its strengths, Envoy has some limitations:

  1. Complexity: Envoy’s extensive feature set and configuration options can be overwhelming for new users. Setting up and tuning Envoy requires expertise, especially in large-scale deployments.
  2. Resource Usage: While Envoy is lightweight compared to alternatives, running a sidecar proxy for every service in a service mesh can increase resource consumption, particularly in resource-constrained environments.
  3. Learning Curve: The xDS APIs and filter system, while powerful, have a steep learning curve for developers unfamiliar with service proxies.
  4. WebAssembly Maturity: While WebAssembly support is promising, it is still maturing, and writing Wasm filters requires additional tooling and expertise.
  5. Dependency on Control Plane: As a data plane, Envoy relies on a control plane for configuration. Misconfigurations in the control plane can lead to outages or degraded performance.

Envoy in 2025: Recent Developments

In 2025, Envoy continues to evolve. Recent updates include:

  • Improved HTTP/3 Support: Full support for HTTP/3 and QUIC, enabling faster, more reliable web communication.
  • Enhanced WebAssembly Integration: Simplified tooling for writing Wasm filters, making extensibility more accessible.
  • Better Observability: Integration with OpenTelemetry has been streamlined, providing richer tracing and metrics.
  • Performance Optimizations: Ongoing work to reduce memory and CPU usage, particularly for sidecar deployments.

The CNCF’s continued investment in Envoy ensures it remains at the forefront of cloud-native networking.

Comparison with Alternatives

Envoy is often compared to other proxies like NGINX, HAProxy, and Traefik. Here’s how it stacks up:

  • NGINX: NGINX is a popular choice for edge proxies and load balancing but lacks Envoy’s service mesh capabilities and dynamic configuration via xDS.
  • HAProxy: HAProxy is a high-performance TCP/HTTP load balancer but is less extensible and lacks native service mesh integration.
  • Traefik: Traefik is a modern proxy with dynamic configuration but is primarily focused on edge use cases and has limited support for non-HTTP protocols.

Envoy’s combination of performance, extensibility, and service mesh integration makes it a stronger choice for cloud-native applications, though NGINX and HAProxy may still be preferred for simpler use cases.

Getting Started with Envoy

To get started with Envoy, follow these steps:

  1. Install Envoy: Download the binary from the official Envoy website or use a package manager like Docker.
  2. Configure Envoy: Write a YAML configuration file defining listeners, routes, and clusters. Alternatively, use a control plane like Istio.
  3. Run Envoy: Start Envoy with the command envoy -c config.yaml.
  4. Integrate with Tools: Set up Prometheus, Grafana, or Jaeger for monitoring and tracing.

The Envoy documentation and community tutorials provide detailed guidance for beginners and advanced users alike.

Conclusion

Envoy is a cornerstone of modern cloud-native architectures, offering unparalleled performance, flexibility, and observability. Its ability to function as an edge proxy, service mesh sidecar, API gateway, and more makes it a versatile tool for organizations of all sizes. While its complexity and resource demands can pose challenges, the benefits of dynamic configuration, advanced load balancing, and robust security far outweigh the drawbacks for most use cases.

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