# Istio Agent

This document describes the internal architecture of Istio agent.

## High Level overview

![High Level overview](docs/overview.svg)

At a high level, the Istio agent acts as an intermediate proxy between Istiod and Envoy. This is done
at two levels. For distributing workload certificates, Envoy will send [SDS](https://www.envoyproxy.io/docs/envoy/latest/configuration/security/secret)

            // Add the agent JAR to the test runtime classpath so the InProcessGradleExecuter can find the module and spawn daemons.
            // This doesn't apply the agent to the test process.
            "${prefix}TestRuntimeOnly"(project(":instrumentation-agent"))
            "${prefix}TestAgentsClasspath"(project(":instrumentation-agent"))
        }
    }
}


internal

LINUX_AGENT_BINARIES:=./cni/cmd/istio-cni \
  ./cni/cmd/install-cni \
  $(AGENT_BINARIES)

BINARIES:=$(STANDARD_BINARIES) $(AGENT_BINARIES) $(LINUX_AGENT_BINARIES)

# List of binaries that have their size tested
RELEASE_SIZE_TEST_BINARIES:=pilot-discovery pilot-agent istioctl envoy ztunnel client server

      throw RuntimeException(failure)
    }

    return countRef.get()
  }

  private fun updateReports() {
    val latch = CountDownLatch(1)
    newWebSocket(
      "/updateReports?agent=$USER_AGENT",
      object : WebSocketListener() {
        override fun onClosing(
          webSocket: WebSocket,
          code: Int,
          reason: String,
        ) {
          webSocket.close(1000, null)

    // US region agents have name "EC2-XXX"
    doesNotContain("teamcity.agent.name", "EC2")
}

/**
 * We have some "shared" host where a Linux build agent and a Windows build agent
 * both run on the same bare metal. Some builds require exclusive access to the
 * hardware resources (e.g. performance test).
 */
fun Requirements.requiresNotSharedHost() {
    doesNotContain("agent.host.type", "shared")
}

    if (cookies.isNotEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies))
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", USER_AGENT)
    }

    val networkRequest = requestBuilder.build()
    val networkResponse = chain.proceed(networkRequest)

    cookieJar.receiveHeaders(networkRequest.url, networkResponse.headers)

class RequestCommonTest {
  @Test
  fun constructorNormal() {
    val url = "https://example.com/".toHttpUrl()
    val body = "hello".toRequestBody()
    val headers = headersOf("User-Agent", "RequestTest")
    val method = "PUT"
    val request =
      Request(
        url = url,
        headers = headers,
        method = method,
        body = body,
      )

  @Test fun ofMapAcceptsEmptyValue() {
    val headers = mapOf("User-Agent" to "").toHeaders()
    assertThat(headers.value(0)).isEqualTo("")
  }

  @Test fun ofMapTrimsKey() {
    val headers = mapOf(" User-Agent " to "OkHttp").toHeaders()
    assertThat(headers.name(0)).isEqualTo("User-Agent")
  }

  @Test fun ofMapTrimsValue() {
    val headers = mapOf("User-Agent" to " OkHttp ").toHeaders()

  val headers: List<String>? by option("-H", "--header", help = "Custom header to pass to server").multiple()

  val userAgent: String by option("-A", "--user-agent", help = "User-Agent to send to server").default(NAME + "/" + versionString())

  val connectTimeout: Int by option(
    "--connect-timeout",
    help = "Maximum time allowed for connection (seconds)",
  ).int().default(DEFAULT_TIMEOUT)

대부분의 표준 헤더는 "마이너스 기호" (`-`)라고도 하는 "하이픈" 문자로 구분됩니다.

그러나 파이썬에서 `user-agent`와 같은 형태의 변수는 유효하지 않습니다.

따라서 `Header`는 기본적으로 매개변수 이름을 언더스코어(`_`)에서 하이픈(`-`)으로 변환하여 헤더를 추출하고 기록합니다.

또한 HTTP 헤더는 대소문자를 구분하지 않으므로 "snake_case"로 알려진 표준 파이썬 스타일로 선언할 수 있습니다.

따라서, `User_Agent` 등과 같이 첫 문자를 대문자화할 필요없이 파이썬 코드에서처럼 `user_agent`로 사용합니다.

만약 언더스코어를 하이픈으로 자동 변환을 비활성화해야 할 어떤 이유가 있다면, `Header`의 `convert_underscores` 매개변수를 `False`로 설정하십시오: