Glossary

Flexway's terms, in alphabetical order, each with the page that explains it. Configuration keys and extension names are written as they are typed.

Admin port

The separate listener (:9090 by default) of the probes, /config, the simulation, the journals and the metrics; never routable from outside. -> Admin API

API key

A secret given to a caller without a token, bound to a tenant and to named operations; the gateway keeps only its SHA-256 digest. -> API keys

Asynchronous plane

Publishing and consuming messages on a broker (Kafka, AMQP, MQTT, NATS) under an AsyncAPI contract, with the same identity and tenant as HTTP. -> Publishing and consuming on a broker

Bucket

A caller's token bucket in a rate-limit policy: it fills at a rate and loses one token per request; empty, 429 rate_limited. -> Setting quotas

Catalogue

The list of served operations, with their upstream, security, owner and withdrawal date, published by /config and shown by the console. -> Reading with the console

Circuit breaker

The per-upstream state that stops calling a failing upstream for a while, then tests it again (upstreams.<name>.circuit_breaker). -> Setting quotas

Closed by default

What is not declared does not pass: operation, header, parameter, origin. The whitelist is the normal mode. -> Security posture

Configuration digest

config_digest: the semantic digest of the configuration served, printed by flexway validate and published by /config, which tells whether two replicas serve the same thing. -> Changing the configuration without a restart

Contract

The document that describes an API - OpenAPI 3.1, AsyncAPI 3, gRPC service or A2A agent card. The contract is the configuration: the gateway serves exactly the operations it declares, and nothing else. -> API gateway

Effective configuration

What a replica serves at this moment: every key of flexway.yaml as loaded, secrets masked, plus the catalogue and the chains, read on GET /config. -> Admin API

Enforced policy

A policy a fragment places at the head of every chain of the gateway that imports it (HTTP listener): no local line removes, replaces or undoes it (since 1.7.0). -> Shared policy fragments

Extension

An x-flexway-* key written in the contract for what belongs to an operation (upstream, timeout, cache, MCP tool...). The list is closed: an unknown extension is refused at load. -> Configuration reference

Host

A host name served with its own contracts and default upstream (hosts), to serve several APIs from one gateway. -> Changing the configuration without a restart

Issuer

An OIDC identity provider declared under auth.issuers, whose tokens the gateway verifies. -> Wiring your identity provider

MCP federation

Existing MCP servers placed behind the gateway's MCP surface, their tools offered under their names, under the same decision as the contract's tools. -> Agents and MCP

MCP surface

The gateway's Model Context Protocol entry point: the operations marked x-flexway-tool are offered there as tools to agents, under the same decision as REST. -> Agents and MCP

Operation

A method on a path of a contract (or a gRPC method), the unit the gateway routes, authorizes, counts and logs. -> Serving your first API

operationId

The unique name of an operation in the contract. Required: quotas, keys, audit and metrics name operations by it. -> Serving your first API

Policy

A named, phased and conditional (CEL) treatment - CORS, rate, quota, cache, transformation, external call... - declared under policies and attached by a chain. -> Enriching a flow

Policy fragment

A kind: PolicyFragment file of policy definitions written once, imported by several gateways that each pin it by its sha256 digest; its definitions are named <import>/<name> there (since 1.7.0). -> Shared policy fragments

Policy chain

The order in which policies apply to an operation: global -> host -> routes -> operation, the most specific wins, a removal is written !name. -> Enriching a flow

Proposal

A change of flexway.yaml prepared in the console, reviewed, then opened as a pull request on the repository that holds the configuration; the console never merges. -> Proposing a change from the console

Quota

A ceiling of requests per tenant per day or month (a quota policy), counted in the shared cache; past it, 429 quota_exceeded. -> Setting quotas

Rate class

The group of operations that shares a caller's bucket in a rate-limit policy (read, write or a declared class); an operation changes class with x-flexway-rate-class. -> Setting quotas

Reload

Reading the configuration and the contracts again without a restart; a refused configuration never replaces the one serving. -> Changing the configuration without a restart

Replica

One instance of the gateway's process. Each replica has its own memory (cache, journals); only the counters are shared, through the shared cache. -> Choosing a deployment

Shared cache

The Redis-compatible shared cache - Redis, Dragonfly or Valkey (server.counters) - where the replicas reconcile buckets and quotas, off the request path; optional, but required by tenant quotas. Its counters are disposable: lost, the gateway goes on with local counters. -> Setting quotas

Shedding

The immediate refusal (503 overloaded) of lower-priority requests when the gateway saturates (server.shedding, x-flexway-priority). -> Setting quotas

SLO

An availability or latency objective, on an operation or a group of operations, followed by the console with its error budget. -> SLO objectives on groups of operations

Tenant

The isolated customer a request belongs to, read from a signed claim, an API key or a certificate - never from a value the caller writes. -> Multi-tenant isolation

Timeout budget

The three timeouts of an exchange - connect, read (the silence tolerated, which alone bounds a stream) and total (retries included) -, from the most general (server.timeouts) to the most specific (x-flexway-timeout on the operation). -> Serving your first API

Token exchange

Obtaining, from the caller's identity provider, a token issued for one specific upstream (RFC 8693): the upstream never receives the original token. -> Agents and MCP

Upstream

The service the gateway relays an operation to, declared under upstreams in flexway.yaml and named by the operation (x-flexway-upstream) or by default (default). An operation without an upstream makes the start fail. -> Serving your first API

Virtual cluster

The Kafka cluster a native client sees through the gateway: declared in the AsyncAPI contract, each tenant reads and writes there under its own names. -> Native Kafka clients