Kong does not allow http1.1 when http2 is enabled

We are using Kong 2.8.3 and have multiple services behind Kong. Some of those services are http services while others are gprc. When we are using gRPC clients for the gRPC services or use http2 to connect http services everything works great.

However, when we send requests via http1.1 clients for our http services, Kong doesn’t work properly. Here are some requests:

failed request: curl --http1.1 ‘https://examplekonghostname/oauth2/token
response: curl: (52) Empty reply from server

successful request: curl ‘https://examplekonghostname/oauth2/token
response: {“error”:“invalid_method”,“error_description”:“The HTTP method GET is invalid for the token endpoint”} (this is expected)

Our Kong configuration:

prefix: /kong_prefix/
database: postgres
ssl_cert: /etc/secrets/secret-tls/tls.crt
ssl_cert_key: /etc/secrets/secret-tls/tls.key
nginx_http_client_max_body_size: 0
nginx_http_client_body_buffer_size: 15000m
nginx_http_client_header_buffer_size: 15000m
log_level: info
proxy_listen: “ http2 reuseport backlog=16384, http2 ssl reuseport backlog=16384”

How can we resolve this issue?