envoyproxy · mattklein123 · Feb 7, 2023 · Oct 11, 2022 · Oct 11, 2022 · Oct 12, 2022
diff --git a/README.md b/README.md
@@ -7,7 +7,8 @@
   - [API Deprecation History](#api-deprecation-history)
 - [Building and Testing](#building-and-testing)
   - [Docker-compose setup](#docker-compose-setup)
-  - [Full test environment](#full-test-environment)
+  - [Full test environment - Configure rate limits through files](#full-test-environment---configure-rate-limits-through-files)
+  - [Full test environment - Configure rate limits through an xDS Management Server](#full-test-environment---configure-rate-limits-through-an-xds-management-server)
   - [Self-contained end-to-end integration test](#self-contained-end-to-end-integration-test)
 - [Configuration](#configuration)
   - [The configuration format](#the-configuration-format)
@@ -25,6 +26,8 @@
       - [Example 6](#example-6)
       - [Example 7](#example-7)
   - [Loading Configuration](#loading-configuration)
+    - [File Based Configuration Loading](#file-based-configuration-loading)
+    - [xDS Management Server Based Configuration Loading](#xds-management-server-based-configuration-loading)
   - [Log Format](#log-format)
   - [GRPC Keepalive](#grpc-keepalive)
 - [Request Fields](#request-fields)
@@ -129,11 +132,12 @@ If you want to run with [two redis instances](#two-redis-instances), you will ne
 the docker-compose.yml file to run a second redis container, and change the environment variables
 as explained in the [two redis instances](#two-redis-instances) section.
 
-## Full test environment
+## Full test environment - Configure rate limits through files
 
 To run a fully configured environment to demo Envoy based rate limiting, run:
 
 ```bash
+export CONFIG_TYPE=FILE
 docker-compose -f docker-compose-example.yml up --build --remove-orphans
 ```
 
@@ -160,6 +164,36 @@ To see the metrics in the example
 curl http://localhost:9102/metrics | grep -i shadow
 ```
 
+## Full test environment - Configure rate limits through an xDS Management Server
+
+To run a fully configured environment to demo Envoy based rate limiting, run:
+
+```bash
+export CONFIG_TYPE=GRPC_XDS_SOTW
+docker-compose -f docker-compose-example.yml --profile xds-config up --build --remove-orphans
+```
+
+This will run in `xds-config` docker-compose profile which will run example xDS-Server, ratelimit, redis, prom-statsd-exporter and two Envoy containers such that you can demo rate limiting by hitting the below endpoints.
+
+```bash
+curl localhost:8888/test
+curl localhost:8888/header -H "foo: foo" # Header based
+curl localhost:8888/twoheader -H "foo: foo" -H "bar: bar" # Two headers
+curl localhost:8888/twoheader -H "foo: foo" -H "baz: baz"  # This will be rate limited
+curl localhost:8888/twoheader -H "foo: foo" -H "bar: banned" # Ban a particular header value
+curl localhost:8888/twoheader -H "foo: foo" -H "baz: shady" # This will never be ratelimited since "baz" with value "shady" is in shadow_mode
+curl localhost:8888/twoheader -H "foo: foo" -H "baz: not-so-shady" # This is subject to rate-limiting because the it's now in shadow_mode
+```
+
+Edit[`examples/xds-sotw-config-server/resource.go`](examples/xds-sotw-config-server/resource.go) to test different rate limit configs.
+
+To see the metrics in the example
+
+```bash
+# The metrics for the shadow_mode keys
+curl http://localhost:9102/metrics | grep -i shadow
+```
+
 ## Self-contained end-to-end integration test
 
 Integration tests are coded as bash-scripts in `integration-test/scripts`.
@@ -492,6 +526,18 @@ descriptors:
 
 ## Loading Configuration
 
+Rate limit service supports following configuration loading methods. You can define which methods to use by configuring environment variable `CONFIG_TYPE`.
+
+| Config Loading Method                                                             | Value for Environment Variable `CONFIG_TYPE` |
+| --------------------------------------------------------------------------------- | -------------------------------------------- |
+| [File Based Configuration Loading](#file-based-configuration-loading)             | `FILE` (Default)                             |
+| [xDS Server Based Configuration Loading](#xds-server-based-configuration-loading) | `GRPC_XDS_SOTW`                              |
+
+When the environment variable `FORCE_START_WITHOUT_INITIAL_CONFIG` set to `false`, the Rate limit service will wait for initial rate limit configuration before
+starting the server (gRPC, Rest server endpoints). When set to `true` the server will start even without initial configuration.
+
+### File Based Configuration Loading
+
 The Ratelimit service uses a library written by Lyft called [goruntime](https://github.com/lyft/goruntime) to do configuration loading. Goruntime monitors
 a designated path, and watches for symlink swaps to files in the directory tree to reload configuration files.
 
@@ -525,6 +571,31 @@ For more information on how runtime works you can read its [README](https://gith
 By default it is not possible to define multiple configuration files within `RUNTIME_SUBDIRECTORY` referencing the same domain.
 To enable this behavior set `MERGE_DOMAIN_CONFIG` to `true`.
 
+### xDS Management Server Based Configuration Loading
+
+xDS Management Server is a gRPC server which implements the [Aggregated Discovery Service (ADS)](https://github.com/envoyproxy/data-plane-api/blob/97b6dae39046f7da1331a4dc57830d20e842fc26/envoy/service/discovery/v3/ads.proto).
+The xDS Management server serves [Discovery Response](https://github.com/envoyproxy/data-plane-api/blob/97b6dae39046f7da1331a4dc57830d20e842fc26/envoy/service/discovery/v3/discovery.proto#L69) with [Ratelimit Configuration Resources](api/ratelimit/config/ratelimit/v3/rls_conf.proto)
+and with Type URL `"type.googleapis.com/ratelimit.config.ratelimit.v3.RateLimitConfig"`.
+The xDS client in the Rate limit service configure Rate limit service with the provided configuration.
+For more information on xDS protocol please refer to the [envoy proxy documentation](https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol).
+
+You can refer to [the sample xDS configuration management server](examples/xds-sotw-config-server/README.md).
+
+The xDS server for listening for configuration can be set via [settings](https://github.com/envoyproxy/ratelimit/blob/master/src/settings/settings.go)
+package with the following environment variables:
+
+```
+CONFIG_GRPC_XDS_NODE_ID default:"default"
+CONFIG_GRPC_XDS_SERVER_URL default:"localhost:18000"
+CONFIG_GRPC_XDS_SERVER_CONNECT_RETRY_INTERVAL default:"3s"
+```
+
+As well Ratelimit supports TLS connections, these can be configured using the following environment variables:
+
+1. `CONFIG_GRPC_XDS_SERVER_USE_TLS`: set to `"true"` to enable a TLS connection with the xDS configuration management server.
+2. `CONFIG_GRPC_XDS_CLIENT_TLS_CERT`, `CONFIG_GRPC_XDS_CLIENT_TLS_KEY`, and `CONFIG_GRPC_XDS_SERVER_TLS_CACERT` to provides files to specify a TLS connection configuration to the xDS configuration management server.
+3. `CONFIG_GRPC_XDS_SERVER_TLS_SAN`: (Optional) Override the SAN value to validate from the server certificate.
+
 ## Log Format
 
 A centralized log collection system works better with logs in json format. JSON format avoids the need for custom parsing rules.

diff --git a/docker-compose-example.yml b/docker-compose-example.yml
@@ -49,6 +49,22 @@ services:
       - RUNTIME_ROOT=/data
       - RUNTIME_SUBDIRECTORY=ratelimit
       - RUNTIME_WATCH_ROOT=false
+      - CONFIG_TYPE=${CONFIG_TYPE:-FILE}
+      - CONFIG_GRPC_XDS_NODE_ID=test-node-id
+      - CONFIG_GRPC_XDS_SERVER_URL=ratelimit-xds-config-server:18000
+
+  ratelimit-xds-config-server:
+    image: ratelimit-xds-config-server:latest
+    build:
+      context: examples/xds-sotw-config-server
+      dockerfile: Dockerfile
+    command: ["-nodeID", "test-node-id", "-port", "18000", "-debug", "true"]
+    expose:
+      - 18000
+    networks:
+      - ratelimit-network
+    profiles:
+      - xds-config
 
   envoy-proxy:
     image: envoyproxy/envoy-dev:latest

diff --git a/examples/xds-sotw-config-server/Dockerfile b/examples/xds-sotw-config-server/Dockerfile
@@ -0,0 +1,11 @@
+FROM golang:1.18 AS build
+WORKDIR /xds-server
+
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux go build -o /go/bin/xds-server -v main/main.go
+
+FROM alpine:3.16 AS final
+RUN apk --no-cache add ca-certificates && apk --no-cache update
+COPY --from=build /go/bin/xds-server /bin/xds-server
+ENTRYPOINT [ "/bin/xds-server" ]
diff --git a/examples/xds-sotw-config-server/README.md b/examples/xds-sotw-config-server/README.md
@@ -0,0 +1,17 @@
+# Example Rate-limit Configuration SotW xDS Server
+
+This is an example of a trivial xDS V3 control plane server similar to the example server in [go-control-plane](https://github.com/envoyproxy/go-control-plane/tree/main/internal/example). It serves sample Rate limit configuration. You can run the example using the project top-level docker-compose-example.yml, e.g.:
+
+```bash
+export CONFIG_TYPE=GRPC_XDS_SOTW
+docker-compose -f docker-compose-example.yml --profile xds-config up --build --remove-orphans
+```
+
+The docker-compose builds and runs the example server along with Rate limit server. The example server serves a configuration defined in [`resource.go`](resource.go). If everything works correctly, you can follow the [examples in project top-level README.md file](../../README.md#examples).
+
+## Files
+
+- [main/main.go](main/main.go) is the example program entrypoint. It instantiates the cache and xDS server and runs the xDS server process.
+- [resource.go](resource.go) generates a `Snapshot` structure which describes the configuration that the xDS server serves to Envoy.
+- [server.go](server.go) runs the xDS control plane server.
+- [logger.go](logger.go) is the logger.
diff --git a/examples/xds-sotw-config-server/go.mod b/examples/xds-sotw-config-server/go.mod
@@ -0,0 +1,20 @@
+module github.com/envoyproxy/ratelimit/examples/xds-sotw-config-server
+
+go 1.18
+
+require (
+	github.com/envoyproxy/go-control-plane v0.10.3-0.20230127155013-72157d335c8f
+	google.golang.org/grpc v1.52.0
+)
+
+require (
+	github.com/census-instrumentation/opencensus-proto v0.4.1 // indirect
+	github.com/cncf/xds/go v0.0.0-20220314180256-7f1daf1720fc // indirect
+	github.com/envoyproxy/protoc-gen-validate v0.9.1 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	golang.org/x/net v0.4.0 // indirect
+	golang.org/x/sys v0.3.0 // indirect
+	golang.org/x/text v0.5.0 // indirect
+	google.golang.org/genproto v0.0.0-20221118155620-16455021b5e6 // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+)
diff --git a/examples/xds-sotw-config-server/go.sum b/examples/xds-sotw-config-server/go.sum
@@ -0,0 +1,73 @@
+cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
+github.com/census-instrumentation/opencensus-proto v0.4.1 h1:iKLQ0xPNFxR/2hzXZMrBo8f1j86j5WHzznCCQxV/b8g=
+github.com/census-instrumentation/opencensus-proto v0.4.1/go.mod h1:4T9NM4+4Vw91VeyqjLS6ao50K5bOcLKN6Q42XnYaRYw=
+github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
+github.com/cncf/xds/go v0.0.0-20220314180256-7f1daf1720fc h1:PYXxkRUBGUMa5xgMVMDl62vEklZvKpVaxQeN9ie7Hfk=
+github.com/cncf/xds/go v0.0.0-20220314180256-7f1daf1720fc/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
+github.com/envoyproxy/go-control-plane v0.10.3-0.20230127155013-72157d335c8f h1:nqACgqiYlDnB0znidh+8uhnQVLeqfW5NyyRfnGibowc=
+github.com/envoyproxy/go-control-plane v0.10.3-0.20230127155013-72157d335c8f/go.mod h1:VnHyVMpzcLvCFt9yUz1UnCwHLhwx1WguiVDV7pTG/tI=
+github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/envoyproxy/protoc-gen-validate v0.9.1 h1:PS7VIOgmSVhWUEeZwTe7z7zouA22Cr590PzXKbZHOVY=
+github.com/envoyproxy/protoc-gen-validate v0.9.1/go.mod h1:OKNgG7TCp5pF4d6XftA0++PMirau2/yoOwVac3AbF2w=
+github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
+github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/prometheus/client_model v0.0.0-20190812154241-14fe0d1b01d4/go.mod h1:xMI15A0UPsDsEKsMN9yxemIoYk6Tm2C1GtYGdfGttqA=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961/go.mod h1:wehouNa3lNwaWXcvxsM5YxQ5yQlVC4a0KAMCusXpPoU=
+golang.org/x/lint v0.0.0-20190313153728-d0100b6bd8b3/go.mod h1:6SW0HCj/g11FgYtHlgUYUwCkIfeOF89ocIRzGO/8vkc=
+golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190213061140-3a22650c66bd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.4.0 h1:Q5QPcMlvfxFTAPV0+07Xz/MpK9NTXu2VDUuy0FeMfaU=
+golang.org/x/net v0.4.0/go.mod h1:MBQ8lrhLObU/6UmLb4fmbmk5OcyYmqtbGd/9yIeKjEE=
+golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
+golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.3.0 h1:w8ZOecv6NaNa/zC8944JTU3vz4u6Lagfk4RPQxv92NQ=
+golang.org/x/sys v0.3.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.5.0 h1:OLmvp0KP+FVG99Ct/qFiL/Fhk4zp4QQnZ7b2U+5piUM=
+golang.org/x/text v0.5.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
+golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
+golang.org/x/tools v0.0.0-20190524140312-2c0ae7006135/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
+google.golang.org/appengine v1.4.0/go.mod h1:xpcJRLb0r/rnEns0DIKYYv+WjYCduHsrkT7/EB5XEv4=
+google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
+google.golang.org/genproto v0.0.0-20190819201941-24fa4b261c55/go.mod h1:DMBHOl98Agz4BDEuKkezgsaosCRResVns1a3J2ZsMNc=
+google.golang.org/genproto v0.0.0-20221118155620-16455021b5e6 h1:a2S6M0+660BgMNl++4JPlcAO/CjkqYItDEZwkoDQK7c=
+google.golang.org/genproto v0.0.0-20221118155620-16455021b5e6/go.mod h1:rZS5c/ZVYMaOGBfO68GWtjOw/eLaZM1X6iVtgjZ+EWg=
+google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
+google.golang.org/grpc v1.23.0/go.mod h1:Y5yQAOtifL1yxbo5wqy6BxZv8vAUGQwXBOALyacEbxg=
+google.golang.org/grpc v1.25.1/go.mod h1:c3i+UQWmh7LiEpx4sFZnkU36qjEYZ0imhYfXVyQciAY=
+google.golang.org/grpc v1.52.0 h1:kd48UiU7EHsV4rnLyOJRuP/Il/UHE7gdDAQ+SZI7nZk=
+google.golang.org/grpc v1.52.0/go.mod h1:pu6fVzoFb+NBYNAvQL08ic+lvB2IojljRYuun5vorUY=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
+google.golang.org/protobuf v1.28.1 h1:d0NfwRgPtno5B1Wa6L2DAG+KivqkdutMf1UhdNx175w=
+google.golang.org/protobuf v1.28.1/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
diff --git a/examples/xds-sotw-config-server/logger.go b/examples/xds-sotw-config-server/logger.go
@@ -0,0 +1,40 @@
+// Copyright 2020 Envoyproxy Authors
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+package example
+
+import (
+	"log"
+)
+
+type Logger struct {
+	Debug bool
+}
+
+func (logger Logger) Debugf(format string, args ...interface{}) {
+	if logger.Debug {
+		log.Printf("[DEBUG] "+format+"\n", args...)
+	}
+}
+
+func (logger Logger) Infof(format string, args ...interface{}) {
+	log.Printf("[INFO]"+format+"\n", args...)
+}
+
+func (logger Logger) Warnf(format string, args ...interface{}) {
+	log.Printf("[WARN] "+format+"\n", args...)
+}
+
+func (logger Logger) Errorf(format string, args ...interface{}) {
+	log.Printf("[ERROR]"+format+"\n", args...)
+}