Struct BackendConfig 

pub struct BackendConfig {

    pub name: String,
    pub transport: TransportType,
    pub command: Option<String>,
    pub args: Vec<String>,
    pub url: Option<String>,
    pub env: HashMap<String, String>,
    pub timeout: Option<TimeoutConfig>,
    pub circuit_breaker: Option<CircuitBreakerConfig>,
    pub rate_limit: Option<RateLimitConfig>,
    pub concurrency: Option<ConcurrencyConfig>,
    pub retry: Option<RetryConfig>,
    pub outlier_detection: Option<OutlierDetectionConfig>,
    pub hedging: Option<HedgingConfig>,
    pub mirror_of: Option<String>,
    pub mirror_percent: u32,
    pub cache: Option<BackendCacheConfig>,
    pub bearer_token: Option<String>,
    pub forward_auth: bool,
    pub aliases: Vec<AliasConfig>,
    pub default_args: Map<String, Value>,
    pub inject_args: Vec<InjectArgsConfig>,
    pub param_overrides: Vec<ParamOverrideConfig>,
    pub expose_tools: Vec<String>,
    pub hide_tools: Vec<String>,
    pub expose_resources: Vec<String>,
    pub hide_resources: Vec<String>,
    pub expose_prompts: Vec<String>,
    pub hide_prompts: Vec<String>,
    pub hide_destructive: bool,
    pub read_only_only: bool,
    pub failover_for: Option<String>,
    pub priority: u32,
    pub canary_of: Option<String>,
    pub weight: u32,
}

Configuration for a single backend MCP server.

Fields

name: String

Unique backend name, used as the namespace prefix for its tools/resources.

transport: TransportType

Transport protocol to use when connecting to this backend.

command: Option<String>

Command for stdio backends

args: Vec<String>

Arguments for stdio backends

url: Option<String>

URL for HTTP backends

env: HashMap<String, String>

Environment variables for subprocess backends

timeout: Option<TimeoutConfig>

Per-backend timeout

circuit_breaker: Option<CircuitBreakerConfig>

Per-backend circuit breaker

rate_limit: Option<RateLimitConfig>

Per-backend rate limit

concurrency: Option<ConcurrencyConfig>

Per-backend concurrency limit

retry: Option<RetryConfig>

Per-backend retry policy

outlier_detection: Option<OutlierDetectionConfig>

Per-backend outlier detection (passive health checks)

hedging: Option<HedgingConfig>

Per-backend request hedging (parallel redundant requests)

mirror_of: Option<String>

Mirror traffic from another backend (fire-and-forget). Set to the name of the source backend to mirror.

mirror_percent: u32

Percentage of requests to mirror (1-100, default: 100).

cache: Option<BackendCacheConfig>

Per-backend cache policy

bearer_token: Option<String>

Static bearer token for authenticating to this backend (HTTP only). Supports ${ENV_VAR} syntax for env var resolution.

forward_auth: bool

Forward the client’s inbound auth token to this backend. Only works with HTTP backends when the proxy has auth enabled.

aliases: Vec<AliasConfig>

Tool aliases: rename tools exposed by this backend

default_args: Map<String, Value>

Default arguments injected into all tool calls for this backend. Merged into tool call arguments (does not overwrite existing keys).

inject_args: Vec<InjectArgsConfig>

Per-tool argument injection rules.

param_overrides: Vec<ParamOverrideConfig>

Per-tool parameter overrides: hide, rename, and inject defaults.

expose_tools: Vec<String>

Capability filtering: only expose these tools (allowlist)

hide_tools: Vec<String>

Capability filtering: hide these tools (denylist)

expose_resources: Vec<String>

Capability filtering: only expose these resources (allowlist, by URI)

hide_resources: Vec<String>

Capability filtering: hide these resources (denylist, by URI)

expose_prompts: Vec<String>

Capability filtering: only expose these prompts (allowlist)

hide_prompts: Vec<String>

Capability filtering: hide these prompts (denylist)

hide_destructive: bool

Hide tools annotated as destructive (destructive_hint = true).

read_only_only: bool

Only expose tools annotated as read-only (read_only_hint = true).

failover_for: Option<String>

Failover: name of the primary backend this is a failover for. When set, this backend’s tools are hidden and requests are only routed here when the primary returns an error.

priority: u32

Failover priority for ordering multiple failover backends. Lower values are preferred (tried first). Default is 0. When multiple backends declare failover_for the same primary, they are tried in ascending priority order until one succeeds.

canary_of: Option<String>

Canary routing: name of the primary backend this is a canary for. When set, this backend’s tools are hidden and requests targeting the primary are probabilistically routed here based on weight.

weight: u32

Routing weight for canary deployments (default: 100). Higher values receive proportionally more traffic.

Implementations

impl BackendConfig

pub fn build_filter(&self, separator: &str) -> Result<Option<BackendFilter>>

Build a BackendFilter from this backend’s expose/hide lists. Returns None if no filtering is configured.

Canary and failover backends automatically hide all capabilities so their tools don’t appear in ListTools responses (traffic reaches them via routing middleware, not direct tool calls).

Trait Implementations

impl Debug for BackendConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for BackendConfig

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for BackendConfig

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.