Are there docs to create custom integration?
No but we’re happy to answer questions about the process here. 
It helps to look at code of existing integrations.
@untitaker thanks for the reply. I’m setting up on-premise docker sentry, and I want to test my custom integration. But the docker logs are only outputting uwsgi logs, and I don’t see uwsgi conf on the sentry repo. I also checked the LOGGING dict from /conf/server.py, it does output the logs to console, but I am unable to see the logs from docker logs, how can I enable logs to stdout?
I have created a global integration for opsgenie, I have this entrypoint here
It’s not being displayed on the organization integration page. Not sure if I’m missing something. Do I have to make some UI changes for it to be visible? Legacy plugins used to be visible by just adding entrypoint.
EDIT: It’s visible now, I had to explicitly register the integration provider by calling register, adding entrypoint was not enough.