What Azure availability zone is used by default when availability options are not specified for VM or other resource? If region consists of several zones, when each zone itself can be one or multiple data centers, when zone or zone redundancy is not set, physically resource should be deployed to one of the zones. Is there a default zone in such case (e.g. zone #1)? How will Azure infrastructure make sure that all those resources are deployed in same or adjacent datacenters?
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If you don't specify any zone, Azure will place your VMs using some internal rule, and it is highly probable that your VMs will end up in different zones
Depending on the region you are working in, this will have more or less impact on the network latencies between your servers. Microsoft does say that traffic between zones inside a region should have ok latencies. In my experience, certain workloads may suffer from this distance, like DB-tier VMs and Web-Tier VMs with intensive query load.
Some features will have the consequence of colocating your VMs. For example for clustered VMs, it is recommended to place them inside an Availability Set, which will have the effect of placing them in the same datacenter, and also ensuring that they are on different Fault Domains (think different hardware). Or Proximity Placement groups too.
K. Shu
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One of the core problems is that Availability Set doesn't support setting specific AZ, which makes it impractical for clustering solutions. E.g. I want to run MSSQL Always-On cluster such that 2 nodes are configured with auto-failover and synchronous replication in Availability Set + Proximity Group (zero data loss and low latency HA pair), while additional nodes in different zones are available for redundancy and reads offloading with async replication and manual failover. – Alex Michel Apr 08 '21 at 21:18