Frequently Asked Questions

Technical Questions

Why do I get HTTP/1.1 503 Service Unavailable when sending messages to the HTTP protocol adapter?

Please check if you have a consumer connected and that your consumer is for the same type of message (telemetry or event) that you are sending.

Why do I get the exception io.vertx.core.VertxException: OpenSSL is not available during startup of a protocol adapter?

Please check if you have set the property nativeTlsRequired in the protocol adapter’s configuration to true. The default Hono containers do not contain netty-tcnative. To enable this option, please follow the explanation in the Admin Guide or build your own container images.

Why do I see ConnectionLimitManager - Connection limit (<VALUE>) exceeded in the logs of a protocol adapter?

The configured maximum number of concurrent connections is exceeded and the protocol adapter refuses to accept more connections to prevent running out of resources. This limit is either configured on the protocol adapter (MQTT, AMQP) or if not set, the protocol adapter determines a reasonable value based on the available resources like memory and CPU.

Why do I see MemoryBasedConnectionLimitStrategy - Not enough memory in the logs of a protocol adapter?

The protocol adapter can not allocate enough memory for handle even a small number of connections reliably. Please provide more memory. To try it anyways, configure the maximum number of concurrent connections, as documented in the Admin Guides of the protocol adapter (MQTT, AMQP).

How do I use client certificates for authentication?

Make sure that you are able to connect to the respective protocol adapter with TLS (see the Admin Guide for configuration). Here is an article, that provides a complete walk-through guide for all required steps. Additionally you can use and adapt the script for the creation of demo certificates in the Hono repository. More information can be found in the User Guide of the protocol adapter (MQTT, HTTP).

Organizational Questions

Will you add feature x to Hono?

To find out about the future development you can have a look at the Roadmap or get in touch with the Hono developers.