限流即限制并发量，限制某一段时间只有指定数量的请求进入后台服务器，遇到流量高峰期或者流量突增时，把流量速率限制在系统所能接受的合理范围之内，不至于让系统被高流量击垮。而Envoy可以通过envoy.filters.http.ratelimit插件实现限流。
限流服务Envoy实现限流需要依赖限速服务，Envoy官方为我们提供了基于Redis和Memcached的限速服务
https://github.com/envoyproxy/ratelimit
我们将其从github下载到本地，来看看其中的docker-compose.yaml的工作模式，我们注意到其中的example文件挂载目录
并且其中还制定了配置目录是example/ratelimit
我们来看看config.yaml和example.yaml的内容，发现其中定义了domain和描述符
所以根据文档的提示，我们在envoy配置中应该命中这些描述符才有效，下面我们通过docker-compose up启动ratelimit服务，启动之前我们需要调整docker-compose.yaml，需要将go mod代理指向国内的代理
启动ratelimit服务
配置Envoy
配置envoy之前我们需要注意一下几点
需要用到envoy.filters.http.ratelimit过滤器
指定其domain为example.yaml中对应的rl
需要为其指定ratelimit服务的cluste
需要为route配置限速规则
具体配置如下
admin: address: socket_address: protocol: TCP address: 0.0.0.0 port_value: 9902 static_resources: listeners: - name: listener_0 address: socket_address: protocol: TCP address: 0.0.0.0 port_value: 10000 filter_chains: - filters: - name: envoy.filters.network.http_connection_manager typed_config: "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager codec_type: AUTO stat_prefix: ingress http_filters: - name: envoy.filters.http.ratelimit typed_config: "@type": type.googleapis.com/envoy.extensions.filters.http.ratelimit.v3.RateLimit domain: rl request_type: both stage: 0 rate_limited_as_resource_exhausted: true failure_mode_deny: false enable_x_ratelimit_headers: DRAFT_VERSION_03 rate_limit_service: grpc_service: envoy_grpc: cluster_name: ratelimit transport_api_version: V3 - name: envoy.filters.http.router typed_config: {} route_config: name: route virtual_hosts: - name: local_service domains: ["*"] routes: - match: prefix: "/" route: cluster: service_envoyproxy_io rate_limits: - actions: - request_headers: header_name: "foo" descriptor_key: "foo" clusters: - name: ratelimit type: STRICT_DNS connect_timeout: 1s lb_policy: ROUND_ROBIN protocol_selection: USE_CONFIGURED_PROTOCOL http2_protocol_options: {} load_assignment: cluster_name: ratelimit endpoints: - lb_endpoints: - endpoint: address: socket_address: address: 192.168.43.94 port_value: 8081 - name: service_envoyproxy_io connect_timeout: 30s type: strict_dns # Comment out the following line to test on v6 networks # dns_lookup_family: V4_ONLY lb_policy: ROUND_ROBIN load_assignment: cluster_name: service_envoyproxy_io endpoints: - lb_endpoints: - endpoint: address: socket_address: address: 192.168.43.94 port_value: 5000