一步一步教你寫kubernetes sidecar

本文分享自華為雲社群《一步一步教你寫kubernetes sidecar》，作者： 張儉。

什麼是sidecar？

sidecar，直譯為邊車。 如上圖所示，邊車就是加裝在摩托車旁來達到擴充功能的目的，比如行駛更加穩定，可以拉更多的人和貨物，坐在邊車上的人可以給駕駛員指路等。邊車模式透過給應用服務加裝一個“邊車”來達到控制和邏輯的分離的目的。

對於微服務來講，我們可以用邊車模式來做諸如 日誌收集、服務註冊、服務發現、限流、鑑權等不需要業務服務實現的控制皮膚能力。通常和邊車模式比較的就是像spring-cloud那樣的sdk模式，像上面提到的這些能力都透過sdk實現。

這兩種實現模式各有優劣，sidecar模式會引入額外的效能損耗以及延時，但傳統的sdk模式會讓程式碼變得臃腫並且升級複雜，控制面能力和業務面能力不能分開升級。

本文的程式碼已經上傳到gitee

sidecar 實現原理

介紹了sidecar的諸多功能，但是，sidecar是如何做到這些能力的呢？

原來，在kubernetes中，一個pod是部署的最小單元，但一個pod裡面，允許執行多個container(容器)，多個container(容器)之間共享儲存卷和網路棧。這樣子，我們就可以多container來做sidecar，或者init-container（初始化容器）來調整掛載卷的許可權

日誌收集sidecar

日誌收集sidecar的原理是利用多個container間可以共用掛載卷的原理實現的，透過將應用程式的日誌路徑掛出，用另一個程式訪問路徑下的日誌來實現日誌收集，這裡用cat來替代了日誌收集，部署yaml模板如下

apiVersion: v1
kind: Pod
metadata:
  name: webserver
spec:
  volumes:
    - name: shared-logs
      emptyDir: {}

  containers:
    - name: nginx
      image: ttbb/nginx:mate
      volumeMounts:
        - name: shared-logs
          mountPath: /opt/sh/openresty/nginx/logs

    - name: sidecar-container
      image: ttbb/base
      command: ["sh","-c","while true; do cat /opt/sh/openresty/nginx/logs/nginx.pid; sleep 30; done"]
      volumeMounts:
        - name: shared-logs
          mountPath: /opt/sh/openresty/nginx/logs

使用kubectl create -f 建立pod，透過kubectl logs命令就可以看到sidecar-container列印的日誌輸出

kubectl logs webserver sidecar-container

轉發請求sidecar

這一節我們來實現，一個給應用程式轉發請求的sidecar，應用程式程式碼如下

use std::io::prelude::*;
use std::net::{TcpListener, TcpStream};

fn main() {
    let listener = TcpListener::bind("127.0.0.1:7878").unwrap();

    for stream in listener.incoming() {
        let stream = stream.unwrap();

        handle_connection(stream);
    }
    println!("Hello, world!");
}

fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024];

    stream.read(&mut buffer).unwrap();

    let contents = "Hello";

    let response = format!(
        "HTTP/1.1 200 OK\r\nContent-Length: {}\r\n\r\n{}",
        contents.len(),
        contents
    );

    println!("receive a request!");
    stream.write(response.as_bytes()).unwrap();
    stream.flush().unwrap();
}

我們再來寫一個sidecar，它會每15秒嚮應用程式發出請求

use std::thread;
use std::time::Duration;

fn main() {
    loop {
        thread::sleep(Duration::from_secs(15));
        let response = reqwest::blocking::get("http://localhost:7878").unwrap();
        println!("{}", response.text().unwrap())
    }
}

透過倉庫下的intput/build.sh指令碼構造映象，執行yaml如下

apiVersion: v1
kind: Pod
metadata:
  name: webserver
spec:
  containers:
    - name: input-server
      image: sidecar-examples:input-http-server

    - name: input-sidecar
      image: sidecar-examples:sidecar-input

透過檢視kubectl logs input input-http-server可以看到input-http-server收到了請求

receive a request!
receive a request!

攔截請求sidecar

應用程式程式碼，它會每15s向localhost發出請求

package com.shoothzj.sidecar

import akka.actor.typed.ActorSystem
import akka.actor.typed.scaladsl.Behaviors
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._

import scala.concurrent.{ExecutionContextExecutor, Future}
import scala.util.{Failure, Success}

object HttpClient {
    def main(args: Array[String]): Unit = {
        while (true) {
            Thread.sleep(15_000L)
            implicit val system: ActorSystem[Nothing] = ActorSystem(Behaviors.empty, "SingleRequest")
            // needed for the future flatMap/onComplete in the end
            implicit val executionContext: ExecutionContextExecutor = system.executionContext

            val responseFuture: Future[HttpResponse] = Http().singleRequest(HttpRequest(uri = "http://localhost:7979/hello"))

            responseFuture
                    .onComplete {
                        case Success(res) => println(res)
                        case Failure(_) => sys.error("something wrong")
                    }
        }
    }
}

我們再來寫一個sidecar，它會攔截http請求並列印日誌

package com.shoothzj.sidecar

import akka.actor.typed.ActorSystem
import akka.actor.typed.scaladsl.Behaviors
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.http.scaladsl.server.Directives._

import scala.concurrent.ExecutionContextExecutor
import scala.io.StdIn

object HttpServer {

    def main(args: Array[String]): Unit = {

        implicit val system: ActorSystem[Nothing] = ActorSystem(Behaviors.empty, "my-system")
        // needed for the future flatMap/onComplete in the end
        implicit val executionContext: ExecutionContextExecutor = system.executionContext

        val route =
            path("hello") {
                get {
                    println("receive a request")
                    complete(HttpEntity(ContentTypes.`text/html(UTF-8)`, "<h1>Say hello to akka-http</h1>"))
                }
            }

        val bindingFuture = Http().newServerAt("localhost", 7979).bind(route)
        while (true) {
            Thread.sleep(15_000L)
        }
    }
}

透過倉庫下的output/build.sh指令碼構造映象，執行yaml如下

apiVersion: v1
kind: Pod
metadata:
  name: output
spec:
  volumes:
    - name: shared-logs
      emptyDir: {}

  containers:
    - name: output-workload
      image: sidecar-examples:output-workload
      imagePullPolicy: Never

    - name: sidecar-output
      image: sidecar-examples:sidecar-output
      imagePullPolicy: Never

透過檢視kubectl logs output output-workload可以看到output-sidecar收到了請求

HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:15:47 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:16:02 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:16:17 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:16:32 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:16:47 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:17:02 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:17:17 GMT),HttpEntity.Strict(text/html; charset=UTF-8,31 bytes total),HttpProtocol(HTTP/1.1))
HttpResponse(200 OK,List(Server: akka-http/10.2.9, Date: Tue, 29 Mar 2022 00:17:32 GMT),HttpEntity.Strict(text/html; charset=

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