On Google’s Global HTTP Load Balancer, each HTTPS target proxy is linked to a certificate. You can use the gcloud tool (pre-installed on GCE images) to update your target proxies with new certificates. But make sure that:
- Your version of gcloud is relatively recent. The target-https-proxies commands were only recently added, so they aren’t present in older versions of gcloud. (Not to be confused with
target-http-proxies, which manges plaintext HTTP sites)
- Your renewal server has API access to Compute Engine resources. You can configure this in your GCE templates, or on a instance-by-instance basis.
You can query gcloud for the current certificate, to check if it’s about to expire. If it is, you can upload your new certificate, then use the
target-https-proxies update command to switch over to the new certificate. You won’t see the changes immediately, but soon, the renewed certificate should be installed globally.
There’s a usage quota of 30 SSL certificates (at least on my account). But if you aren’t too aggressive with your renewals, you won’t have any problems even if your renewal script doesn’t clean out expired certificates. It’d be a good idea to keep around at least 1 old certificate, just in case something goes wrong and you need to revert.