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Ansible conditionals let a playbook decide, for each host and each loop item, whether a task should run. The main keyword is when: give it a raw Jinja expression, and Ansible executes the task only where that expression is true. Facts, ordinary variables, and results registered by earlier tasks are the usual inputs.
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This guide shows the syntax that works reliably, how conditions interact with loops, imports, failure and change reporting, and check mode, plus a methodical way to diagnose skipped or unexpectedly executed tasks.
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A task without a condition is eligible to run on every host targeted by the play. A task with when is evaluated separately for each host after Ansible has the variables and facts needed by the expression. A false expression produces a skipped task on that host; it does not make the play fail.
Conditions are decisions, not text substitutions. The value of when, failed_when, and changed_when is already passed through Jinja2, so do not wrap the expression in {{ }}. The following is valid:
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- name: Install a Debian-family package
ansible.builtin.package:
name: nginx
state: present
when: ansible_facts['os_family'] == 'Debian'Adding {{ }} inside the condition can produce warnings or incorrect evaluation because those delimiters are for templating a value into a string, not for an expression field.
Writing when expressions
One condition
Use a Boolean comparison directly. Facts are commonly addressed through the ansible_facts mapping:
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ansible.builtin.debug:
msg: Running the Red Hat family branch
when: ansible_facts['os_family'] == 'RedHat'You can test a variable, a fact, a registered result, or the result of a filter. If the value might not exist, make that possibility explicit rather than allowing an undefined-variable error.
Several conditions with implicit and
A YAML list under when means every entry must be true. This is usually easier to read than a long line:
- name: Enable a feature on supported production hosts
ansible.builtin.service:
name: myapp
state: started
when:
- app_enabled | bool
- environment == 'production'
- ansible_facts['os_family'] in ['Debian', 'RedHat']List entries are combined with implicit and. Do not add the word and between list items.
Using and, or, and parentheses
For alternative branches or custom grouping, use a single expression. Parentheses make the intended precedence clear:
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ansible.builtin.template:
src: compatibility.conf.j2
dest: /etc/myapp/compatibility.conf
when: (ansible_facts['distribution'] == 'Ubuntu' and ansible_facts['distribution_major_version'] | int >= 22) or legacy_mode | boolWithout parentheses, a reader has to remember operator precedence and may misunderstand the branch. Keep complicated logic in an intermediate variable when it can be named meaningfully.
Comparing numbers safely
Facts can arrive as strings. Cast a release or threshold before comparing it numerically:
- name: Use the modern repository on supported releases
ansible.builtin.apt_repository:
repo: deb http://example.invalid/myapp stable main
state: present
when: ansible_facts['lsb']['major_release'] | int >= 6Use | int for whole numbers and | float for decimal measurements. A lexical comparison can otherwise treat values such as 10 and 9 in the wrong order.
Facts and variables as condition inputs
Operating-system facts
The most useful platform facts include ansible_facts['distribution'], ansible_facts['distribution_major_version'], and ansible_facts['os_family']. Choose the fact that matches the decision: an OS family is appropriate for package-manager differences, while an exact distribution or major version is appropriate for a distribution-specific behavior.
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Facts are host attributes collected by Ansible, but no fact is universal across every target, connection type, or fact-gathering configuration. Verify that a key exists on the systems you manage before making it a hard prerequisite for a task. If fact gathering is disabled, these values will not be available unless you gather them explicitly.
Fact freshness
ansible_date_time represents the time at which facts were gathered and cached for that host. In a long-running playbook it can become stale. For a time value that must reflect the current moment, obtain it at the point of use rather than treating ansible_date_time as a live clock.
Normalize a decision with set_fact
When the same test appears in several tasks, calculate a clearly named intermediate value once:
- name: Determine whether this host needs the high-temperature profile
ansible.builtin.set_fact:
needs_high_temperature_profile: >-
{{ (temperature | default(0) | float) > 90 }}
- name: Deploy the high-temperature profile
ansible.builtin.template:
src: high-temperature.conf.j2
dest: /etc/myapp/profile.conf
when: needs_high_temperature_profileThe expression in the set_fact value is a normal templated value, so delimiters are appropriate there. They are not appropriate in the later when expression.
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Separate platform data from branching logic
If a playbook accumulates many distribution-specific conditions, separate variable files, templates, or task files can be clearer than deeply nested expressions. A small, well-named platform variable can leave the task itself with one simple condition and make unsupported platforms obvious.
Conditionals based on registered results
Register a task result
register stores the result of a task in a host-level variable for the current playbook run. Common fields include stdout, stdout_lines, rc, failed, changed, and skipped. A later task can branch on those fields:
- name: Check whether the marker exists
ansible.builtin.command: test -f /etc/myapp/marker
register: marker_check
failed_when: false
- name: Rebuild only when the marker is absent
ansible.builtin.command: /usr/local/bin/rebuild-myapp
when: marker_check.rc != 0The first command normally returns a nonzero code when the file is absent. failed_when: false keeps that expected probe from stopping the play, while the registered return code remains available for the next condition.
Use result tests
Ansible supplies tests that make status checks readable: is failed, is succeeded, is skipped, and is changed. For example:
- name: Report a successful probe
ansible.builtin.debug:
msg: The probe completed
when: probe_result is succeeded
- name: Handle a failed probe
ansible.builtin.debug:
msg: The probe needs attention
when: probe_result is failedAnsible registers a result for each host even when the task failed or was skipped. That lets later tasks inspect status, but it does not make a missing field safe: check the shape of the result before reading a field that a particular module or execution path may not provide.
Registered variables are not persistent facts
A registered variable lives in memory for the current playbook run and is scoped as host-level data. It is not a cache that will be available on a later run. Persist information deliberately if a future run must make a decision from it.
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Inspect command output
Use stdout for the complete text or stdout_lines for a line list. When matching text, make the test explicit and account for the command’s return code as a separate concern:
- name: Check the configured mode
ansible.builtin.command: /usr/local/bin/myapp --show-mode
register: mode_check
changed_when: false
- name: Deploy the fallback configuration
ansible.builtin.template:
src: fallback.conf.j2
dest: /etc/myapp/config.conf
when: mode_check.stdout | trim != 'managed'Using when with loops
When a task has both a loop and a condition, Ansible evaluates the condition separately for each item. Some items can run while others are skipped:
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- name: Print only non-privileged ports
ansible.builtin.debug:
msg: '{{ item }}'
loop: [80, 8080, 8443]
when: item > 1024The item value is available to the expression as item. This per-item behavior is different from a single condition around the whole task: the task can produce a mixture of executed and skipped iterations.
Protect optional loop sources
If a list is optional, default it to an empty list so the task has no iterations instead of failing while resolving an undefined variable:
- name: Configure optional listeners
ansible.builtin.template:
src: listener.conf.j2
dest: '/etc/myapp/listeners/{{ item }}.conf'
loop: '{{ mylist | default([]) }}'For dictionary data, use an empty mapping and test the value you need:
- name: Enable declared features
ansible.builtin.command: '/usr/local/bin/myapp enable {{ item.key }}'
loop: '{{ feature_map | default({}) | dict2items }}'
when: item.value | boolRead loop results correctly
When a registered task runs in a loop, the registered variable contains a results list with one response per item. Inspect item.results in a later task, or loop over that list with a different loop variable to avoid ambiguity.
For per-iteration logic that refers to a result from a previous iteration, provide a default for the first iteration. There is no previous result on that first pass, so an unguarded lookup can fail before the condition has a chance to evaluate.
Defining failure with failed_when
failed_when overrides a module’s normal failure decision. This is useful when a command has several meaningful exit codes, or when a nonzero code is expected and should be handled by a later task.
- name: Query application status without stopping on an expected state
ansible.builtin.command: /usr/local/bin/app status
register: app_status
changed_when: false
failed_when: app_status.rc not in [0, 3]Here, return codes 0 and 3 are accepted; any other code fails the task. The explicit rule documents the contract better than allowing a generic command failure to decide.
Multiple entries in a YAML list under failed_when use implicit and semantics, just like a list under when:
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failed_when:
- app_status.rc not in [0, 3]
- 'fatal' in app_status.stdoutUse a single expression with or when either condition should fail the task. Pair register with ignore_errors: true when a failure must be recorded and then evaluated by later conditional handling. ignore_errors is different from redefining failure: it allows the play to continue after Ansible marks the task failed.
Defining change with changed_when
changed_when overrides the module’s normal change report. Command and shell tasks often need this because a successful command does not necessarily mean that system state changed.
- name: Query application status without reporting a change
ansible.builtin.command: /usr/local/bin/app status
register: app_status
changed_when: false
failed_when: app_status.rc not in [0, 3]You can report a change only when output indicates that work occurred:
- name: Refresh the application index
ansible.builtin.command: /usr/local/bin/app refresh
register: refresh_result
changed_when: refresh_result.rc == 0 and 'updated' in refresh_result.stdoutAs with failed_when, list entries are joined with implicit and. Correct change reporting matters to handlers, summaries, audits, and any automation that uses the changed status as a signal.
Conditionals on imports, includes, and roles
Static imports
A condition on a static import is applied to all tasks in the imported file. The imported tasks are expanded predictably as part of playbook parsing, so the same condition can affect every task in that file:
- name: Load Debian tasks
ansible.builtin.import_tasks: debian.yml
when: ansible_facts['os_family'] == 'Debian'This is convenient when the entire file belongs to one platform branch. Remember that the condition is inherited by each imported task; a task that changes a variable does not retroactively alter how the already-expanded branch is selected.
Dynamic includes
A dynamic include is evaluated at runtime. Variables can change before the include is reached, and the include decision is made then:
- name: Load platform tasks at runtime
ansible.builtin.include_tasks: platform.yml
when: platform_tasks_enabled | boolChoose an import for predictable static expansion and an include when the decision must occur dynamically or when the included content depends on state established earlier in the play.
Roles
Conditions can also be attached when reusing a role. Put the platform or environment decision at the reuse boundary when the whole role is optional; keep task-level conditions inside the role for decisions that vary between individual tasks. This keeps the role’s interface understandable and avoids repeating the same branch on every task.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check mode and conditional branches
Check mode simulates changes. Run it with:
ansible-playbook site.yml --checkSupported modules report what they would change without modifying remote systems. Add diff mode when the module supports it to see proposed file differences.
check_mode: true forces an individual task to run in check mode. check_mode: false forces normal execution for that task even when the playbook was launched with --check. Use the latter sparingly, because it intentionally performs a real operation during a simulation.
A check-mode run cannot always provide ordinary registered-result output. If a preceding task is skipped or does not execute its normal operation in simulation, a later condition that depends on its registered fields may have no useful data. Design such branches with an explicit check-mode path, or guard access to optional result data.
- name: Show the planned action when the probe has run
ansible.builtin.debug:
msg: The marker probe returned {{ marker_check.rc }}
when:
- not ansible_check_mode
- marker_check is definedThis example deliberately avoids reading a result that may not exist during a pure simulation. The exact approach depends on whether the command is safe and supported in check mode.
A complete conditional playbook pattern
The following example combines platform facts, a registered probe, per-item filtering, and explicit failure and change semantics:
---
- name: Configure the application
hosts: app
become: true
tasks:
- name: Gather the normal host facts
ansible.builtin.setup:
- name: Install the Debian-family package
ansible.builtin.package:
name: nginx
state: present
when: ansible_facts['os_family'] == 'Debian'
- name: Check whether the application is already initialized
ansible.builtin.command: test -f /etc/myapp/initialized
register: initialization_check
failed_when: false
changed_when: false
- name: Initialize the application
ansible.builtin.command: /usr/local/bin/myapp init
when:
- initialization_check.rc != 0
- not ansible_check_mode
- name: Configure enabled ports
ansible.builtin.template:
src: port.conf.j2
dest: '/etc/myapp/ports/{{ item }}.conf'
loop: '{{ app_ports | default([]) }}'
when:
- item | int > 1024
- app_ports_enabled | default(true) | bool
- name: Query service status
ansible.builtin.command: /usr/local/bin/myapp status
register: service_status
changed_when: false
failed_when: service_status.rc not in [0, 3]
- name: Start the service when it is stopped
ansible.builtin.service:
name: myapp
state: started
when: service_status.rc == 3The probe tasks are intentionally non-changing, the expected status code is accepted, the loop has a safe default, and initialization is excluded from check mode because it is an operation rather than a simulation.
Why a conditional is skipped or fails
The expression contains {{ }}
Remove the delimiters from when, failed_when, and changed_when. Those fields already evaluate Jinja expressions.
The fact or variable is absent
Inspect the available data and confirm fact gathering. A fact name that exists on one operating system may not exist on another. Use default only when the fallback is semantically safe; a default that silently selects the wrong platform can be more dangerous than a deliberate failure.
A number is being compared as text
Cast release numbers and measurements with | int or | float before comparing them.
A registered result has an unexpected shape
Inspect the complete result, then choose the correct field: stdout, stdout_lines, rc, failed, skipped, or, for loops, results. A task that was skipped may have status metadata but no command output.
An optional loop variable is undefined
Use loop: {{ mylist | default([]) }} for optional lists and default({}) for optional mappings. In actual YAML, the expression is quoted as shown in the examples so the complete templated value is parsed consistently.
Check mode removed the data needed by the branch
Remember that simulation can skip or alter the task that would have populated a registered result. Test the normal run and check-mode run separately, and add an explicit check-mode guard when the operation cannot produce meaningful simulated output.
Quick Recap
A practical debugging checklist
- Display the relevant data with
ansible.builtin.debug: var=ansible_factsor a targeted variable. - Confirm that the condition is a raw expression and contains no
{{ }}. - Verify that strings, integers, and floating-point values are being compared as the intended types.
- For registered results, inspect
stdout,rc,failed,skipped, and loopresults. - Add
default([])ordefault({})to genuinely optional loop inputs. - Run
ansible-playbook site.yml --checkand account for branches that depend on results unavailable during simulation. - Read the skip reason in Ansible’s verbose output; it often identifies the evaluated expression or the missing variable.
Choosing the right conditional pattern
| Decision need | Recommended pattern | Important behavior |
|---|---|---|
| Different operating-system behavior | Fact-based when |
Evaluated independently for every host; verify the fact exists. |
| Several requirements must all hold | YAML list under when |
Entries use implicit and semantics. |
| Alternative branches or custom grouping | One expression with and, or, and parentheses |
Parentheses document precedence and prevent accidental grouping. |
| Decision based on an earlier command | register plus a later condition |
Results are host-level and temporary; skipped or check-mode tasks may not provide normal output. |
| Only some loop items qualify | when alongside loop |
The condition is evaluated separately for each item. |
| One platform file should always share a branch | Conditioned static import | The condition applies to all tasks in the imported file. |
| Branch selection must use runtime state | Conditioned dynamic include | The include is evaluated when execution reaches it. |
| A command’s exit code is not its true failure rule | failed_when |
Define accepted and rejected outcomes explicitly. |
| A successful command should not always report change | changed_when |
Accurate change status improves idempotence reporting and handler behavior. |
| Preview supported changes | --check, optionally with diff mode |
Registered-result-dependent branches may lack data in simulation. |
Key rules to remember
whenis a raw Jinja expression evaluated per host; omit{{ }}.- Facts, ordinary variables, and registered results are the normal sources for decisions.
- Lists of conditions mean implicit
and; use a single expression when you needoror explicit grouping. - Cast strings before numeric comparisons.
- Loop conditions run per item, and optional loop data should have safe defaults.
- Registered variables last only for the current playbook run and contain a
resultslist when the task used a loop. failed_whenandchanged_whenlet you define outcome semantics instead of relying on a command’s default status.- Check mode is a simulation, and it may not populate the registered data that a later conditional expects.
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