Monitoring with tokio-console

Optional support is included to monitor the async runtime using tokio-console. When enabled, a separate tracing subscriber will be installed to monitor when the async runtime polls tasks, and expose that information to diagnostic tools via a gRPC server. Currently, this requires both changes to the aggregator configuration and to the build flags used at compilation. Add a stanza similar to the following to the configuration file.

logging_config:
  tokio_console_config:
    enabled: true
    listen_address: 127.0.0.1:6669

Compile with the tokio-console feature enabled, and provide the flag --cfg tokio_unstable to rustc, as follows. (If tokio-console support is enabled in a build without the tokio_unstable flag, the server will panic upon startup)

RUSTFLAGS="--cfg tokio_unstable" CARGO_TARGET_DIR=target/tokio_unstable cargo build --features tokio-console

Install tokio-console, run the server, and run tokio-console http://127.0.0.1:6669 to connect to it and monitor tasks.