# 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)

  @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()

    assertFailsWith<NullPointerException> {
      (mapOf("User-Agent" to null) as Map<String, String>).toHeaders()
    }
  }

  @Test fun toMultimapGroupsHeaders() {
    val headers =
      Headers.headersOf(
        "cache-control",
        "no-cache",
        "cache-control",
        "no-store",
        "user-agent",
        "OkHttp",
      )
    val headerMap = headers.toMultimap()

OkHttpClient client = new OkHttpClient.Builder()
    .addInterceptor(new LoggingInterceptor())
    .build();

Request request = new Request.Builder()
    .url("http://www.publicobject.com/helloworld.txt")
    .header("User-Agent", "OkHttp Example")
    .build();

Response response = client.newCall(request).execute();
response.body().close();
```

    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)

import vcsroots.useAbsoluteVcs

object WarmupEc2Agent : BuildType({
    name = "Warmup EC2 Agent"
    id("Util_WarmupEc2Agent")

    vcs.useAbsoluteVcs(VersionedSettingsBranch.fromDslContext().vcsRootId())

    features {
        freeDiskSpace {
            // Lower the limit such that the agent work directories aren't cleaned during the AMI baking process
            requiredSpace = "100mb"
        }
    }

Envoy Version:       0.0.0

NAME                                                                SERVICE FQDN                          PORT     SUBSET     DIRECTION       TYPE       DESTINATION RULE
cluster/agent                                                       cluster/agent                         -        -          -               STATIC     

istio.VERSION
LICENSES.txt
# Proxy generated proxy config in integration test
tests/integration/component/proxy/envoy.conf
**/var/run/secrets/
# Certs generated by testing
security/cmd/node_agent/na/cert_file
security/cmd/node_agent/na/pkey
# istioctl bash completion file
tools/istioctl.bash
vendor
# Contains the built artifacts
out/
etc/
var/
# Go compiled tests
*.test
# Profiles
*.prof

`Header` ✔️ 🐥 ➕ 🛠️ 🔛 🔝 ⚫️❔ `Path`, `Query` & `Cookie` 🚚.

🌅 🐩 🎚 🎏 "🔠" 🦹, 💭 "➖ 🔣" (`-`).

✋️ 🔢 💖 `user-agent` ❌ 🐍.

, 🔢, `Header` 🔜 🗜 🔢 📛 🦹 ⚪️➡️ 🎦 (`_`) 🔠 (`-`) ⚗ & 📄 🎚.

, 🇺🇸🔍 🎚 💼-😛,, 👆 💪 📣 👫 ⏮️ 🐩 🐍 👗 (💭 "🔡").

, 👆 💪 ⚙️ `user_agent` 👆 🛎 🔜 🐍 📟, ↩️ 💆‍♂ 🎯 🥇 🔤 `User_Agent` ⚖️ 🕳 🎏.

🚥 🤔 👆 💪 ❎ 🏧 🛠️ 🎦 🔠, ⚒ 🔢 `convert_underscores` `Header` `False`:

=== "🐍 3️⃣.6️⃣ & 🔛"

Portanto, você pode usar `user_agent` como faria normalmente no código Python, em vez de precisar colocar as primeiras letras em maiúsculas como `User_Agent` ou algo semelhante.

Se por algum motivo você precisar desabilitar a conversão automática de sublinhados para hífens, defina o parâmetro `convert_underscores` de `Header` para `False`: