basher83 Ansible Error Handling
Patterns for robust error handling in Ansible playbooks and roles.
Block/Rescue/Always Pattern
Handle errors and perform cleanup:
- name: Deploy application
block:
- name: Stop application
ansible.builtin.systemd:
name: myapp
state: stopped
- name: Deploy new version
ansible.builtin.copy:
src: myapp-v2.0
dest: /usr/bin/myapp
- name: Start application
ansible.builtin.systemd:
name: myapp
state: started
rescue:
- name: Rollback to previous version
ansible.builtin.copy:
src: myapp-backup
dest: /usr/bin/myapp
- name: Start application (rollback)
ansible.builtin.systemd:
name: myapp
state: started
- name: Report failure
ansible.builtin.fail:
msg: "Deployment failed, rolled back to previous version"
always:
- name: Cleanup temp files
ansible.builtin.file:
path: /tmp/deploy-*
state: absent
Execution Flow
- block: Main tasks execute sequentially
- rescue: Runs if ANY task in block fails
- always: Runs regardless of success/failure
Retry with Until
Handle transient failures with retries:
- name: Wait for service to be ready
ansible.builtin.uri:
url: http://localhost:8080/health
status_code: 200
register: health_check
until: health_check.status == 200
retries: 30
delay: 10
# Total wait: up to 5 minutes (30 * 10s)
With Command Module
- name: Wait for cluster to stabilize
ansible.builtin.command: pvecm status
register: cluster_status
until: "'Quorate: Yes' in cluster_status.stdout"
retries: 12
delay: 5
changed_when: false
Retry Parameters
| Parameter | Description |
|---|---|
until |
Condition that must be true to stop retrying |
retries |
Maximum number of attempts |
delay |
Seconds between attempts |
Assert for Validation
Validate inputs with clear error messages:
- name: Validate required variables
ansible.builtin.assert:
that:
- vm_name is defined
- vm_name | length > 0
- vm_memory >= 1024
- vm_cores >= 1
fail_msg: |
Invalid VM configuration:
- vm_name: {{ vm_name | default('NOT SET') }}
- vm_memory: {{ vm_memory | default('NOT SET') }} (min: 1024)
- vm_cores: {{ vm_cores | default('NOT SET') }} (min: 1)
success_msg: "VM configuration validated"
quiet: true
Common Assertions
# Variable defined and non-empty
- vm_name is defined and vm_name | trim | length > 0
# Numeric range
- vm_memory >= 1024 and vm_memory <= 65536
# Regex match
- vm_name is match('^[a-z0-9-]+$')
# List has items
- vm_networks | length > 0
# Value in allowed list
- vm_ostype in ['l26', 'win10', 'win11']
Fail with Context
Provide actionable error messages:
- name: Check prerequisites
ansible.builtin.command: which docker
register: docker_check
changed_when: false
failed_when: false
- name: Fail if Docker not installed
ansible.builtin.fail:
msg: |
Docker is not installed on {{ inventory_hostname }}.
To install Docker:
sudo apt update
sudo apt install docker.io
Or use the docker role:
ansible-playbook playbooks/install-docker.yml
when: docker_check.rc != 0
Graceful Failure Handling
Allow expected "failures":
- name: Try to stop service
ansible.builtin.systemd:
name: myservice
state: stopped
register: stop_result
failed_when:
- stop_result.failed
- "'not found' not in stop_result.msg"
# Only fail if error is NOT "service not found"
Multiple Acceptable Conditions
- name: Join cluster
ansible.builtin.command: pvecm add {{ primary_node }}
register: cluster_join
failed_when:
- cluster_join.rc != 0
- "'already in a cluster' not in cluster_join.stderr"
- "'cannot join' not in cluster_join.stderr"
changed_when: cluster_join.rc == 0
Check Before Fail
Separate checking from failing for better control:
- name: Check if resource exists
ansible.builtin.command: check-resource {{ resource_id }}
register: resource_check
changed_when: false
failed_when: false # Don't fail here
- name: Fail with context if missing
ansible.builtin.fail:
msg: |
Resource {{ resource_id }} not found.
Command output: {{ resource_check.stderr }}
Hint: Ensure resource was created first.
when: resource_check.rc != 0
Error Recovery Pattern
Attempt operation, handle specific errors:
- name: Attempt primary approach
block:
- name: Connect via primary endpoint
ansible.builtin.uri:
url: "https://{{ primary_host }}:8006/api2/json"
validate_certs: true
register: primary_result
rescue:
- name: Log primary failure
ansible.builtin.debug:
msg: "Primary endpoint failed: {{ primary_result.msg | default('unknown error') }}"
- name: Try fallback endpoint
ansible.builtin.uri:
url: "https://{{ fallback_host }}:8006/api2/json"
validate_certs: false
register: fallback_result
Delegate Error Handling
Run checks from controller for better error context:
- name: Verify API endpoint from controller
ansible.builtin.uri:
url: "https://{{ inventory_hostname }}:8006/api2/json/version"
validate_certs: false
delegate_to: localhost
register: api_check
failed_when: false
- name: Report API status
ansible.builtin.fail:
msg: |
Cannot reach Proxmox API on {{ inventory_hostname }}
Status: {{ api_check.status | default('connection failed') }}
Check: Network connectivity, firewall rules, pveproxy service
when: api_check.status | default(0) != 200
Ignore Errors (Use Sparingly)
- name: Remove optional backup
ansible.builtin.file:
path: /backup/old-backup.tar.gz
state: absent
ignore_errors: true
register: cleanup_result
- name: Report cleanup status
ansible.builtin.debug:
msg: "Cleanup {{ 'successful' if not cleanup_result.failed else 'skipped' }}"
When ignore_errors is Acceptable
- Non-critical cleanup tasks
- Optional operations that shouldn't block playbook
- When the result is immediately checked anyway
Prefer failed_when
# BETTER than ignore_errors
- name: Remove backup
ansible.builtin.file:
path: /backup/old-backup.tar.gz
state: absent
register: cleanup_result
failed_when:
- cleanup_result.failed
- "'does not exist' not in cleanup_result.msg | default('')"
Complete Example
---
- name: Deploy with comprehensive error handling
hosts: app_servers
become: true
tasks:
- name: Validate configuration
ansible.builtin.assert:
that:
- app_version is defined
- app_version is match('^\d+\.\d+\.\d+$')
fail_msg: "Invalid app_version: {{ app_version | default('NOT SET') }}"
- name: Deploy application
block:
- name: Download release
ansible.builtin.get_url:
url: "https://releases.example.com/{{ app_version }}.tar.gz"
dest: /tmp/app.tar.gz
register: download
until: download is succeeded
retries: 3
delay: 5
- name: Stop current version
ansible.builtin.systemd:
name: myapp
state: stopped
- name: Extract release
ansible.builtin.unarchive:
src: /tmp/app.tar.gz
dest: /opt/myapp
remote_src: true
- name: Start new version
ansible.builtin.systemd:
name: myapp
state: started
- name: Verify health
ansible.builtin.uri:
url: http://localhost:8080/health
register: health
until: health.status == 200
retries: 6
delay: 10
rescue:
- name: Restore previous version
ansible.builtin.copy:
src: /opt/myapp-backup/
dest: /opt/myapp/
remote_src: true
- name: Start previous version
ansible.builtin.systemd:
name: myapp
state: started
- name: Report deployment failure
ansible.builtin.fail:
msg: |
Deployment of {{ app_version }} failed.
Previous version restored.
Check logs: journalctl -u myapp
always:
- name: Cleanup download
ansible.builtin.file:
path: /tmp/app.tar.gz
state: absent
Additional Resources
For detailed error handling patterns and techniques, consult:
references/error-handling.md- Comprehensive error handling patterns, block/rescue/always examples, retry strategies
Related Skills
- ansible-idempotency - changed_when/failed_when patterns
- ansible-fundamentals - Core Ansible concepts