Configuration

Configure Agentgateway with YAML or JSON files. Covers static config, local file-watch config, and XDS dynamic config.

Agentgateway is configured through YAML or JSON files (the two formats are fully equivalent). Configuration is split into three forms: static config for global process settings, local config for full proxy configuration with hot-reload, and XDS config for remote control plane management.

File format

Configuration files use the following top-level structure:

# yaml-language-server: $schema=https://agentgateway.dev/schema/config

# Global process settings (static — requires restart to change)
config:
  logging:
    format: json
  adminAddr: "0.0.0.0:9901"

# Traffic configuration (dynamic — hot-reloaded on file change)
binds:
- port: 3000
  listeners:
  - routes:
    - backends:
      - host: upstream:8080

Adding the # yaml-language-server comment at the top of your config file enables schema validation and autocompletion in editors that support the YAML Language Server.

JSON is fully equivalent to YAML:

config.yaml

binds:
- port: 3000
  listeners:
  - routes:
    - backends:
      - host: upstream:8080

{
  "binds": [
    {
      "port": 3000,
      "listeners": [
        {
          "routes": [
            {
              "backends": [
                { "host": "upstream:8080" }
              ]
            }
          ]
        }
      ]
    }
  ]
}

Static configuration

The config block contains settings that are read once at startup. These control global behaviors that apply to the entire process.

config:
  # Logging
  logging:
    format: json          # "json" or "text"
    level: info           # trace, debug, info, warn, error

  # Observability servers
  adminAddr: "0.0.0.0:9901"      # Admin UI
  statsAddr: "0.0.0.0:9902"      # Prometheus metrics
  readinessAddr: "0.0.0.0:9903"  # Readiness probe

  # DNS resolver
  dns:
    lookupFamily: Auto    # All, Auto, V4Preferred, V4Only, V6Only

  # OpenTelemetry tracing
  tracing:
    otlpEndpoint: "http://otel-collector:4317"
    randomSampling: "0.1"  # 10% sampling (CEL expression)

  # Backend connection pool
  backend:
    connectTimeout: 10s
    poolIdleTimeout: 90s
    poolMaxSize: 100

  # Session management
  session:
    key: "<openssl rand -hex 32>"  # AES-256-GCM key for session tokens

Static configuration changes require a process restart. Use local config or XDS for anything that needs to change at runtime.

Static config reference

Field	Description
config.logging.format	Log format: json or text
config.logging.level	Log level: trace, debug, info, warn, error
config.adminAddr	Admin UI address (ip:port)
config.statsAddr	Prometheus metrics address (ip:port)
config.readinessAddr	Readiness probe address (ip:port)
config.dns.lookupFamily	IP family preference for DNS lookups
config.tracing.otlpEndpoint	OTLP endpoint for OpenTelemetry traces
config.tracing.randomSampling	CEL expression evaluating to 0.0–1.0 or bool
config.backend.connectTimeout	Upstream connection timeout
config.backend.poolMaxSize	Max idle connections per host
config.session.key	AES-256-GCM key for encrypted session tokens
config.workerThreads	Number of async worker threads
config.enableIpv6	Enable IPv6 support

Local configuration

The dynamic part of the configuration — binds, listeners, routes, backends, and policies — lives outside the config block. When you run Agentgateway with a config file, it watches the file for changes and hot-reloads the configuration without restarting.

File watch reloads

1. Initial load

   At startup, Agentgateway reads the config file and translates it into the Internal Representation (IR). The proxy begins handling traffic.

2. File change detected

   When the file is modified (saved), the file watcher detects the change and re-reads the file.

3. Validation and translation

   The new configuration is validated and translated into a new IR. If validation fails, the old configuration stays in place and an error is logged.

4. Atomic swap

   The new IR atomically replaces the old one. In-flight requests complete against the old configuration. New requests use the new configuration.

You can also point config.localXdsPath to a separate file that contains only the dynamic configuration (binds, listeners, routes, backends). This keeps static and dynamic config cleanly separated.

Configuration hierarchy

The dynamic configuration follows a strict hierarchy: binds → listeners → routes → backends, with policies attachable at the route level.

Binds

A Bind defines a TCP port to listen on.

binds:
- port: 3000        # Required: TCP port number
  listeners: [...]  # One or more listeners on this port

Listeners

A Listener defines how connections on a port are handled. Multiple listeners on the same port are distinguished by hostname.

binds:
- port: 3000
  listeners:
  - name: my-listener
    hostname: api.example.com    # Optional; supports wildcards
    protocol: http               # http (default)
    tls:
      cert: /certs/tls.crt
      key: /certs/tls.key
      minTLSVersion: "1.2"
    routes: [...]

Field	Description
name	Optional listener name
hostname	Hostname to match; supports wildcards like *.example.com
protocol	Protocol: http
tls.cert	Path to TLS certificate
tls.key	Path to TLS private key
tls.minTLSVersion	Minimum TLS version (1.2 or 1.3)
tls.maxTLSVersion	Maximum TLS version (1.2 or 1.3)
tls.cipherSuites	Optional cipher suite allowlist (order preserved)

Routes

A Route matches incoming requests and applies policies before forwarding to backends.

routes:
- name: my-route
  hostnames:
  - api.example.com
  matches:
  - path:
      pathPrefix: /v1/
    method: GET
    headers:
    - name: x-api-version
      value:
        exact: "2"
  policies:
    cors:
      allowOrigins: ["*"]
    auth:
      jwt:
        issuer: https://auth.example.com
  backends:
  - host: api-service:8080

Match types:

Match type	Fields	Description
Path	exact, pathPrefix, regex	Match by request path
Header	name + exact or regex	Match by header value
Method	method	Match by HTTP method
Query	name + exact or regex	Match by query parameter

Backends

A Backend defines an upstream target. The type is inferred from the fields you provide.

HTTP backend

backends:
- host: api-service:8080

MCP backend

backends:
- mcp:
    targets:
    - name: everything
      stdio:
        cmd: npx
        args: ["@modelcontextprotocol/server-everything"]

A2A backend

backends:
- host: localhost:9999

With the a2a: {} policy on the route to mark it as A2A traffic:

policies:
  a2a: {}

Policies

Policies are attached at the route level and control authentication, authorization, rate limiting, observability, and traffic shaping.

routes:
- policies:
    # CORS
    cors:
      allowOrigins: ["*"]
      allowHeaders: ["mcp-protocol-version", "content-type", "cache-control"]
      exposeHeaders: ["Mcp-Session-Id"]

    # JWT authentication
    auth:
      jwt:
        issuer: https://auth.example.com
        jwksUri: https://auth.example.com/.well-known/jwks.json

    # CEL-based authorization
    authz:
      rules:
      - expression: 'jwt.sub == "allowed-user"'

    # Rate limiting
    rateLimit:
      requests: 100
      window: 60s
  backends:
  - host: upstream:8080

Real-world examples

Basic MCP proxy (basic/config.yaml)

# yaml-language-server: $schema=https://agentgateway.dev/schema/config
binds:
- port: 3000
  listeners:
  - routes:
    - policies:
        cors:
          allowOrigins:
          - "*"
          allowHeaders:
          - mcp-protocol-version
          - content-type
          - cache-control
          exposeHeaders:
          - "Mcp-Session-Id"
      backends:
      - mcp:
          targets:
          - name: everything
            stdio:
              cmd: npx
              args: ["@modelcontextprotocol/server-everything"]

config:
  logging:
    format: json
frontendPolicies:
  accessLog:
    add:
      backend: backend
binds:
- port: 3000
  listeners:
  - routes:
    - policies:
        cors:
          allowOrigins:
          - '*'
          allowHeaders:
          - content-type
          - cache-control
        # Mark this route as A2A traffic
        a2a: {}
      backends:
      - host: localhost:9999

Architecture

Understand how static config, local config, and XDS map to the proxy’s Internal Representation

CEL expressions

Write authorization rules and transformation expressions using CEL