How do I configure flow control?

There are three knobs for configuring Envoy flow control: listener limits, and http2 stream limits

The listener limits are also propogated to the HttpConnectionManager, and applied on a per-stream basis to HTTP/1.1 L7 buffers described below. As such they limit the size of HTTP/1 requests and response bodies that can be buffered. For HTTP/2, as many streams can be multiplexed over one TCP connection, the L7 and L4 buffer limits can be tuned separately, and the configuration option is applied to all of the L7 buffers. Note that for both HTTP/1 and HTTP/2 Envoy can and will proxy arbitrarily large bodies on routes where all L7 filters are streaming, but many filters such as the transcoder or buffer filters require the full HTTP body to be buffered, so limit the request and response size based on the listener limit.

The following code block shows how to adjust all three fields mentioned above, though generally the only one which needs to be amended is the listener per_connection_buffer_limit_bytes