OCI - Q and A - Compute

 

🔰 Basic Level

1. What is OCI Compute?

Answer:
OCI Compute is an Infrastructure-as-a-Service (IaaS) offering that allows you to launch and manage virtual machines (VMs) and bare metal servers to run your applications and workloads in Oracle Cloud.

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2. What are the types of compute instances in OCI?

Answer:

• Bare Metal: Dedicated physical server.

• Virtual Machine (VM): Shared compute instance.

• Dedicated VM Host: Your own server to host multiple VM instances.

• Container Instances: Lightweight OCI-managed container hosting.

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3. What are shapes in OCI Compute?

Answer:
A shape determines the resources (CPU, memory, network) allocated to a compute instance. Examples:

• Standard: General purpose

• Dense I/O: High-performance storage

• GPU: For machine learning and AI

• High-Performance Computing (HPC)

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4. What is an instance pool in OCI?

Answer:
An instance pool lets you manage a group of identical compute instances that scale automatically. Useful for load-balanced or parallel processing workloads.

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5. What operating systems are supported in OCI compute?

Answer:
OCI supports:

• Oracle Linux

• Red Hat Enterprise Linux

• Ubuntu

• CentOS

• Windows Server

• Custom images

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⚙️ Intermediate Level

6. What is the difference between boot volume and block volume in OCI?

Answer:

• Boot Volume: Stores the OS and is used to boot the instance.

• Block Volume: Additional storage attached to an instance for data storage.

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7. Can you resize a compute instance in OCI?

Answer:
Yes, by stopping the instance, changing the shape, and then restarting it.

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8. What are custom images in OCI compute?

Answer:
Custom images are snapshots of existing instances, including OS and apps, used to launch new instances with the same configuration.

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9. What is a preemptible instance?

Answer:
A preemptible instance is a cost-effective compute option that can be terminated by Oracle after 24 hours or earlier if capacity is needed.

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10. What are the common lifecycle states of a compute instance?

Answer:

• Provisioning

• Running

• Stopping

• Stopped

• Terminating

• Terminated

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🧠 Advanced & Scenario-Based Questions

11. How would you secure a compute instance in OCI?

Answer:

• Use Network Security Groups (NSGs) or Security Lists

• Restrict inbound ports (e.g., SSH - 22)

• Apply OCI IAM policies

• Enable instance OS-level firewall (iptables/firewalld)

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12. Scenario: You cannot SSH into a compute instance. What steps will you take?

Answer:

1. Check VCN security list and NSG rules.

2. Ensure port 22 is open and public IP is assigned.

3. Verify SSH key pair and username (e.g., opc for Oracle Linux).

4. Use OCI Serial Console for root-level recovery.

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13. What are placement groups (affinity/anti-affinity) in OCI?

Answer:
Fault Domains (FDs) are used to spread instances across different hardware in the same Availability Domain for high availability. You can configure affinity or anti-affinity rules using instance pools or orchestration scripts.

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14. How do you create a compute instance using CLI in OCI?

Answer:

oci compute instance launch \
  --compartment-id <compartment-ocid> \
  --availability-domain <AD> \
  --shape VM.Standard2.1 \
  --display-name "MyInstance" \
  --image-id <image-ocid> \
  --subnet-id <subnet-ocid> \
  --ssh-authorized-keys-file ~/.ssh/id_rsa.pub

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15. What is the difference between public and private IP in OCI?

Answer:

• Public IP: Internet-accessible IP address.

• Private IP: Internal VCN IP used within OCI network.

You can assign reserved public IPs for persistence across restarts.

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16. How do you connect two compute instances privately across regions?

Answer:

• Set up VCN peering (Local or Remote)

• Use Dynamic Routing Gateway (DRG) for remote peering

• Ensure routing tables and security rules are properly configured

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17. Scenario: A compute instance is running, but application is unreachable. Troubleshoot.

Answer:

• Ping private/public IP.

• Check:

  • Security List/NSG

  • Subnet route tables

  • Application port (e.g., 80/443)

  • Firewall on OS

  • Web server status (e.g., Apache/Nginx)

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18. What happens when you terminate a compute instance?

Answer:

• Instance is deleted permanently

• Boot volume is also deleted unless configured to preserve

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19. How do you automate provisioning of compute in OCI?

Answer:

• Use Terraform

• Use OCI CLI scripting

• Use Resource Manager (OCI native Terraform service)

• Use OCI SDKs (Python, Java, etc.)

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20. What is the role of Availability Domain (AD) and Fault Domain (FD) in Compute?

Answer:

• AD: A physical datacenter within a region.

• FD: A logical grouping to protect against hardware failure within an AD.

• Placing instances in different FDs increases fault tolerance.