As OpenResty is going to release 1.21.4, it is time to consider dropping the support of Tengine.
Although Tengine is still maintained (a bugfix is just merged this month), IMHO there will be some benefits if we can drop the support of Tengine: 1. The latest Tengine is still based on Nginx 1.18.0, which is released years ago. 2. The Tengine support of APISIX is contributed by a contributor who is no longer active. The maintainers don't have much experience to work with Tengine. 3. Some feature of Tengine, like Dubbo proxy, is already supported in apisix-base. 4. Some feature of APISIX requires apisix-base, which is not supported by Tengine. By dropping the support of Tengine, we can remove extra CI job and version check, make the code simpler. In the future, we may only support OpenResty 1.19+. What about your opinion?
