I am currently working on Sitecore (9.0.2) implementation on Azure PAAS. Sitecore can take a lot of advantages on Azure PAAS. Be it setting up environments quickly, Maintaining your resources (on your own or with the help of Cloud Solution Provider -CSP), Scaling, and Monitoring.
Troubleshooting of Sitecore on Azure sometimes became complicated and different then your own Infrastructure. I am stating few ways troubleshooting your Sitecore implementation on Azure PAAS based on my recent experience.
Instance not coming up
After setting up initial single setup on Azure PAAS for our Dev environment, we were required to restart the Webapp either manually in case of any issue or automatically as part of deployment process from Octopus. After performing the restart on Webapp, it was showing Running in Azure portal as shown below:
But when i access the Sitecore instance, i was facing The 503 Service Unavailable error.
Even after restarting the Webapp multiple times, result was the same. It shows running in azure portal. But Sitecore instance could not come up.