OCI Compute — Launch, Manage & Scale

Overview

Provision and manage OCI compute instances using the Python SDK. Compute is the entry point for most OCI workloads, but "out of host capacity" errors, shape selection confusion (Flex vs Standard, AMD vs ARM vs Intel), and boot volume management make it harder than AWS EC2. This skill covers shape selection, launch with capacity retry across availability domains, instance lifecycle actions, and boot volume management.

Purpose: Launch reliable compute instances with retry logic that survives capacity shortages.

Prerequisites

• OCI Python SDK — pip install oci
• Config file at ~/.oci/config with fields: user, fingerprint, tenancy, region, key_file
• IAM policy — Allow group Developers to manage instances in compartment <name>
• Python 3.8+
• A VCN with at least one subnet (see oraclecloud-core-workflow-b)

Instructions

Step 1: Understand Shape Options

Shape	Arch	Flex?	OCPUs	Use Case
VM.Standard.A1.Flex	ARM (Ampere)	Yes	1-80	Always Free eligible, best price/perf
VM.Standard.E5.Flex	AMD	Yes	1-94	General purpose, broadest availability
VM.Standard3.Flex	Intel	Yes	1-32	Intel-specific workloads
VM.Standard.E4.Flex	AMD	Yes	1-64	Previous gen, still available

Key rule: Always use Flex shapes. They let you set exact OCPU and memory. Standard (non-Flex) shapes have fixed sizes and are being phased out.

Step 2: List Available Shapes and Images

import oci

config = oci.config.from_file("~/.oci/config")
compute = oci.core.ComputeClient(config)
identity = oci.identity.IdentityClient(config)

# Get availability domains
ads = identity.list_availability_domains(compartment_id=config["tenancy"]).data

# List shapes in each AD
for ad in ads:
    shapes = compute.list_shapes(
        compartment_id=config["tenancy"],
        availability_domain=ad.name
    ).data
    flex_shapes = [s for s in shapes if "Flex" in s.shape]
    print(f"\n{ad.name}:")
    for s in flex_shapes:
        print(f"  {s.shape} | OCPUs: {s.ocpu_options.min}-{s.ocpu_options.max}")

Step 3: Launch with Capacity Retry

The most common OCI error is 500 InternalError with message "Out of host capacity." The fix is to retry across availability domains.

import oci
import time

config = oci.config.from_file("~/.oci/config")
compute = oci.core.ComputeClient(config)
identity = oci.identity.IdentityClient(config)

ads = identity.list_availability_domains(compartment_id=config["tenancy"]).data

launch_details = oci.core.models.LaunchInstanceDetails(
    compartment_id=config["tenancy"],
    display_name="my-app-server",
    shape="VM.Standard.A1.Flex",
    shape_config=oci.core.models.LaunchInstanceShapeConfigDetails(
        ocpus=2, memory_in_gbs=12
    ),
    source_details=oci.core.models.InstanceSourceViaImageDetails(
        image_id="ocid1.image.oc1...",  # Oracle Linux 8 image OCID
        boot_volume_size_in_gbs=50
    ),
    create_vnic_details=oci.core.models.CreateVnicDetails(
        subnet_id="ocid1.subnet.oc1..."
    ),
    metadata={"ssh_authorized_keys": open("/home/user/.ssh/id_rsa.pub").read()},
)

# Retry across all ADs on capacity errors
for ad in ads:
    launch_details.availability_domain = ad.name
    try:
        response = compute.launch_instance(launch_details)
        print(f"Launched in {ad.name}: {response.data.id}")
        break
    except oci.exceptions.ServiceError as e:
        if e.status == 500 and "capacity" in str(e.message).lower():
            print(f"No capacity in {ad.name}, trying next AD...")
            time.sleep(2)
            continue
        raise
else:
    print("ERROR: No capacity in any AD. Try a different shape or region.")

Step 4: Instance Lifecycle Actions

instance_id = "ocid1.instance.oc1..."

# Stop (SOFTSTOP sends ACPI shutdown, STOP is hard power-off)
compute.instance_action(instance_id=instance_id, action="SOFTSTOP")

# Start
compute.instance_action(instance_id=instance_id, action="START")

# Reboot
compute.instance_action(instance_id=instance_id, action="SOFTRESET")

# Terminate (preserves boot volume by default)
compute.terminate_instance(
    instance_id=instance_id,
    preserve_boot_volume=True
)

Step 5: Get Instance Metadata and Public IP

# Get instance details
instance = compute.get_instance(instance_id=instance_id).data
print(f"State: {instance.lifecycle_state}")
print(f"Shape: {instance.shape}")

# Get VNIC attachments to find public IP
network = oci.core.VirtualNetworkClient(config)
vnic_attachments = compute.list_vnic_attachments(
    compartment_id=config["tenancy"],
    instance_id=instance_id
).data

for attachment in vnic_attachments:
    vnic = network.get_vnic(vnic_id=attachment.vnic_id).data
    print(f"Public IP: {vnic.public_ip}")
    print(f"Private IP: {vnic.private_ip}")

Output

Successful completion produces:

• A running compute instance in the best available AD
• Capacity retry logic that falls back across availability domains
• Instance lifecycle management (stop, start, reboot, terminate)
• Public and private IP addresses retrieved via VNIC attachment

Error Handling

Error	Code	Cause	Solution
Out of host capacity	500 InternalError	AD has no available hosts for shape	Retry across ADs (Step 3), try different shape, or different region
Not authenticated	401 NotAuthenticated	Bad API key or config	Verify ~/.oci/config key_file path and fingerprint
Not authorized	404 NotAuthorizedOrNotFound	IAM policy missing or wrong OCID	Add IAM policy: Allow group X to manage instances in compartment Y
Shape not found	400 InvalidParameter	Shape not available in region	List shapes first (Step 2) to confirm availability
Rate limited	429 TooManyRequests	Too many API calls	Add exponential backoff; OCI does not return Retry-After header
Limit exceeded	400 LimitExceeded	Service limit for shape reached	Request limit increase in Console > Governance > Limits

Examples

Quick instance list via CLI:

# List all running instances
oci compute instance list \
  --compartment-id <OCID> \
  --lifecycle-state RUNNING \
  --query "data[*].{Name:\"display-name\",Shape:shape,State:\"lifecycle-state\"}" \
  --output table

Find Oracle Linux images:

images = compute.list_images(
    compartment_id=config["tenancy"],
    operating_system="Oracle Linux",
    shape="VM.Standard.A1.Flex",
    sort_by="TIMECREATED",
    sort_order="DESC",
).data
latest = images[0]
print(f"Latest image: {latest.display_name} ({latest.id})")

Resources

• Compute Service Overview — launching and managing instances
• Python SDK Reference — ComputeClient API
• CLI Reference — oci compute commands
• Always Free Tier — ARM A1 Flex instances included
• Known Issues — current service issues

Next Steps

After launching instances, proceed to oraclecloud-core-workflow-b to build the networking layer (VCN, subnets, security rules), or see oraclecloud-data-handling for Object Storage operations.