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Orchestration — Heat

Heat is the OpenStack Orchestration service. It provisions and manages stacks of cloud resources defined in declarative templates. A single Heat Orchestration Template (HOT) can describe compute instances, networks, subnets, routers, floating IPs, security groups, volumes, load balancers, and auto-scaling groups — along with all the dependency relationships between them. Heat manages the full lifecycle: create, update, suspend, resume, check, and delete.

Heat has been a core OpenStack service since the Icehouse release (2014). The convergence engine (parallel, graph-based resource operations) replaced the legacy sequential stack engine in Newton (2016).

When to Read This Skill

  • Writing HOT templates to provision multi-tier application infrastructure
  • Understanding how Heat resolves resource dependency graphs
  • Creating or managing environments (parameter defaults, resource type mappings)
  • Debugging stack failures and inspecting resource events
  • Implementing auto-scaling with OS::Heat::AutoScalingGroup and OS::Heat::ScalingPolicy
  • Delivering software configuration to instances via OS::Heat::SoftwareConfig and OS::Heat::SoftwareDeployment
  • Implementing wait conditions and resource signaling
  • Understanding the convergence engine vs legacy stack lifecycle
  • Configuring heat.conf for production deployments
  • Writing custom resource plugins

Sub-Files

File What It Covers
architecture.md heat-api, heat-api-cfn, heat-engine; HOT template format and sections; resource types; environments; convergence architecture; inter-service integration
operations.md CLI and API: stack create/update/delete/check/suspend/resume, resource inspection, event querying, output retrieval, template validation; complete HOT template example; environment files; config reference
internals.md Resource plugin interface; built-in resource types; dependency graph resolution; convergence engine; stack lock mechanism; nested stacks; resource signaling; software deployment chain

Quick Reference

# Validate a template before deploying
openstack orchestration template validate -t web-app.yaml

# Create a stack
openstack stack create \
  -t web-app.yaml \
  -e prod-env.yaml \
  --parameter db_password=secret123 \
  web-app-stack

# Watch stack progress
openstack stack event list --follow web-app-stack

# List all stacks
openstack stack list

# Show stack details and outputs
openstack stack show web-app-stack
openstack stack output show web-app-stack floating_ip

# Update a stack in place
openstack stack update \
  -t web-app-v2.yaml \
  -e prod-env.yaml \
  web-app-stack

# Check real-world resource status vs Heat's recorded state
openstack stack check web-app-stack

# Suspend all stack resources
openstack stack suspend web-app-stack

# Resume a suspended stack
openstack stack resume web-app-stack

# Delete a stack and all its resources
openstack stack delete web-app-stack

# List resources in a stack
openstack stack resource list web-app-stack

# Inspect a specific resource
openstack stack resource show web-app-stack web_server

# List nested stack events
openstack stack event list --nested-depth 2 web-app-stack

# Show the template stored for a running stack
openstack stack template show web-app-stack

Dependencies

Dependency Purpose Notes
Keystone Authentication, service catalog, and trust delegation Heat creates Keystone trusts so that deferred operations (e.g. auto-scaling) can act as the stack owner
Nova Provisioning OS::Nova::Server resources Most stacks include at least one server
Neutron Provisioning OS::Neutron::* resources (networks, subnets, routers, floating IPs, security groups) Required for any stack with networking resources
Cinder Provisioning OS::Cinder::Volume and OS::Cinder::VolumeAttachment Required for stacks with persistent block storage
Glance Resolving image names/IDs for Nova servers Used indirectly through Nova
Octavia Provisioning OS::Octavia::LoadBalancer resources Optional; required for LBaaS stacks
RabbitMQ (or oslo.messaging backend) RPC between heat-api and heat-engine Required; all engine calls go through the message bus
MariaDB 10.6+ or PostgreSQL 14+ Heat database (stacks, resources, events, software configs) Required
Memcached Token and policy caching Strongly recommended
python-heatclient / python-openstackclient CLI and Python bindings openstack stack * commands use the Heat v1 REST API

Releases Covered

This skill covers OpenStack 2025.1 (Epoxy), 2025.2, and 2026.1.

Heat release notes: https://docs.openstack.org/releasenotes/heat/