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This article mainly introduces how Envoy is started, the content of the article is carefully selected and edited by the author, with a certain pertinence, for everyone's reference significance is still relatively great, the following with the author to understand how Envoy is started.

Functional Overview

When Envoy starts, it starts a process and starts many threads in this process, so that many worker threads can be started. Generally, the number of worker threads is the same as the number of cores. Each worker thread processes requests on all configured listener, manages connections and handles filterchain, non-blocking. At the same time, a main thread is started in this process, which is responsible for starting and stopping envoy, which is also a thread that provides configuration management through API, and it collects different metrics, manages other threads, and is also non-blocking.

Important data structure definition

2.1 Filter

Filters, including listener filter, network filter, and http filter. Listener filter can be used to operate connection metadata and operate on newly received sockets, such as obtaining the original destination address, redirecting connections, etc.; network filter is mainly responsible for data reading and writing; http filter is mainly responsible for data processing.

2.2 Listener

Listeners. Envoy supports configuring any number of listeners in each thread, and each listener can configure a certain number of network filter independently. You can also optionally configure listener filter,listener filter to process before the connection is established, and network filter to process after the connection is established.

2.3 Worker

A worker corresponds to a thread of envoy execution. The listener is bound to the worker, and the worker is responsible for listening, filtering and forwarding. The life cycle of each connection is bound to a separate worker. In general, envoy achieves 100% non-blocking.

Code flow

3.1 process Overview

When Envoy starts, it first starts the main thread, initializes listener and filter in the main thread, then binds listener to worker, and the main thread pulls up the worker thread, and the worker thread is responsible for listening for new connections.

3.2 initialization

3.2.1 main entry

The main function is the total entry point for envoy startup. The main_common is generated first for subsequent initialization.

3.2.2 initialize main_common

In main_common will generate maincommonbase, it will do server instance initialization, an instance is an instance of a service.

3.2.3 Instance initialization

After calling the InstanceImpl function in maincommonbase, first register the configuration information carried by startup, and then perform the initialization of instance.

The initialization of Instance consists of two parts:

① registers the current instance with ListenerManager to manage updates

② creates and initializes MainImpl,MainImpl to initialize listening listener

MainImpl takes a list of static snooping listener based on the configuration file, instantiates them, and registers them with ListenerManager.

3.2.4 initializing listener

Tener, create a ListenerFilterFactoryList for it according to the configuration file, and add ListenerFilterFactory to it according to the configuration.

There are three listener filter: original dst filter,proxy protocol filter, TLS inspector filter, one by one according to the configuration to determine whether to join the ListenerFilterFactoryList.

When you configure the ListenerFilterFactoryList, a NetworkerFilterFactoryList is created for the listener based on the configuration for subsequent connections established on the listener.

3.3 start

3.3.1 launch entry

After the main_common initialization completes normally, the main_common → run () startup is executed, which subsequently executes the run () method of instance, and the run () method of instance performs listener initialization at the network level.

3.3.2 start worker and bind listener to worker

Here, all listener read from the configuration file is bound to all worker. Worker is the service's concurrent thread, which is generally the same as the number of cores. After binding listener to worker, it is initialized through the connectionhandler module.

3.3.3 Listener initialization

The initialization process of Listener first generates ActiveListener, and then initializes listener at the network level by calling the creation function in the network package through ActiveListener.

3.3.5 start the worker thread and enter listening

Listener is bound to worker. When the listener is initialized, you need to start the worker service to enter the listening process.

Here, start a new thread for each worker, and call libevent's event_base_loop to listen. After waiting for the connection event to arrive and trigger, the callback onAccept enters the processing flow.

After reading the above about how Envoy is started, many readers must have some understanding. If you need to get more industry knowledge and information, you can continue to follow our industry information column.

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