Often when I republish a webjob with some minor changed and try to Rerun a Webjob function SCM shows me the following warning in the web portal, and I cannot execute the function
Host is not running; requests will be queued but not execute until the host is started.
The host is always running in this case, and the job is setup as singleton, there should not be a problem with multiple hosts.
The WebJobs Dashboard shows this message until it receives an updated "heartbeat" message from the host indicating that the host is running. The JobHost writes the heartbeat message into blob storage (in the azure-webjobs-hosts container under path /heartbeats). The Dashboard polls the heartbeat blob for a particular host ID and shows this message when it detects the host hasn't started running yet. There might be a minimal delay between when the host starts up and when the Dashboard sees the blob update.