Memory hook: Template repeats; group repairs; disk preserves.
Must remember
Compute Engine provides VMs when OS-level control, custom software or specific hardware is required. Choose machine family, CPU/memory, region/zone, disks, service account and network deliberately. Custom machine types can fit unusual CPU-to-memory ratios. Spot VMs trade lower cost for interruption risk and suit fault-tolerant work.
Boot and data disks have independent lifecycle choices. Persistent disks/Hyperdisk variants have scope, performance and attachment limits; local SSD is ephemeral and should not be the only durable copy. A snapshot supports disk recovery, an image supports reusable boot provisioning, and a machine image captures broader instance configuration/data for supported use cases. Check consistency and retention, not only whether a snapshot job completed.
An instance template defines repeatable VM configuration. A managed instance group (MIG) maintains instances from a template, supports autoscaling, rolling updates and autohealing. Regional MIGs distribute across zones. Load-balancer health checks control traffic; autohealing checks can recreate instances, so thresholds and initial delay should avoid destructive false positives.
Use OS Login for IAM-managed Linux login where supported. Identity-Aware Proxy can provide controlled tunnel access to private instances with the right IAM and firewall configuration. VM Manager supports inventory, patch and OS-configuration operations. Avoid scattering reusable SSH private keys or broad service-account privileges across instances.
Verify inventory, instance status, attached disks, serial/boot logs, service-account permissions and application listeners. Stopping a VM does not necessarily stop all attached-storage or reserved-address charges. Deleting a VM does not guarantee every separately retained disk, snapshot or image disappears.
Review details
Persistent Disk is available in zonal and regional forms; a regional disk replicates across two zones within its region. Replication is not a backup against application deletion. Filestore is managed NFS file storage, Cloud Storage is object storage, and a disk is block storage: choose by application access semantics, not only capacity. Hyperdisk performance/attachment capabilities depend on its type and supported VM.
An unmanaged instance group gathers independently managed VMs for supported use cases; it does not provide a MIG's template-driven desired state and autohealing. A regional MIG still needs a resilient external database/session design. When changing templates, select rolling-update disruption/surge and validate readiness before removing old capacity.
Choose under exam pressure
| Requirement | Choice and reason |
|---|---|
| Stateless fleet across zones | Regional MIG, template, health checks and load balancing. |
| Interruptible batch processing | Spot VMs with checkpointing/retry design. |
| Reusable standardized boot environment | A controlled image plus instance template. |
Traps
- Autoscaling, autohealing and load balancing perform different jobs.
- A retained data disk can continue billing after its VM is deleted.
Active recall
1. What makes a MIG repeatable?
Its instance template and managed desired configuration.
2. What happens to unhealthy autohealed instances?
They can be recreated, making persistent external state and suitable health thresholds important.
3. Snapshot versus image?
A snapshot is primarily disk recovery history; an image supports reusable disk/boot creation.
4. Why use OS Login?
To manage supported VM login permissions through IAM rather than distributing static keys broadly.
5. What must a Spot workload tolerate?
Interruption and capacity unavailability, using retries/checkpoints as appropriate.