I am designing a backup and restore process for API Management. I was hoping to use immutability policy as an extra level of security over the backup files, ensuring that it is impossible to accidentally or intentionally tamper with or delete backups. Backup works fine without, but when I set the policy the following error message is emitted on backup:
2021-09-22T16:47:54.4076381Z ERROR: InvalidParameters: Invalid parameter: This operation is not permitted as the blob is immutable due to a policy.
I can see the operation writes the first 22 bytes, and I assume expects to be able to update the blob with more data, which counts as modifying an existing blob and is not permitted.
Allowing appends doesn't make any difference, presumably because the operation doesn't create an append blob but a block blob. This is not that surprising, but I'd like to know whether I should expect this to be possible, or whether there is any prospect of the product being updated to support this. Backups do seem to be a good use case for the immutability feature so I'd like it to be supported.