Http2

Scenario

Users can easily enable Http2 protocol for better performance through configuration.

The configuration for external service communication is in the microservice.yaml file.

Enable h2(Http2 + TLS)

Append sslEnabled=true to the listening address to enable TLS communication on server side. For details, see the section Using TLS Communication. Then add protocol=http2 to enable h2 communication. Here is the sample configuration:
```
servicecomb:
  rest:
    address: 0.0.0.0:8080?sslEnabled=true&protocol=http2
```
Enable h2c(Http2 without TLS)

Simply add protocol=http2 to enable h2c communication in the server's configuration:
```
servicecomb:
  rest:
    address: 0.0.0.0:8080?protocol=http2
```
The client will read the server's address configuration from service center, then communicate with the server by http2 protocol.

Specific examples can refer to http2-it-tests

configuration	default	description	notice
servicecomb.rest.server.http2.useAlpnEnabled	true	Whether to enable ALPN
servicecomb.rest.server.http2.concurrentStreams	100	The maximum stream concurrency supported in a connection	The smaller value of the concurrentStreams on the server side and the multiplexingLimit on the client side

configuration	default	description	notice
servicecomb.rest.client.http2.useAlpnEnabled	true	Whether to enable ALPN
servicecomb.rest.client.http2.multiplexingLimit	-1	The maximum stream concurrency supported in a connection,-1 means no limit	The smaller value of the concurrentStreams on the server side and the multiplexingLimit on the client side
servicecomb.rest.client.http2.maxPoolSize	1	The maximum number of connections established for each IP:Port in each connection pool
servicecomb.rest.client.http2.idleTimeoutInSeconds	0	The timeout period of the idle connection, the connection will be closed after the timeout