Ansible templates are UTF-8 text files that combine fixed configuration text with Jinja2 expressions. An ansible.builtin.template task renders the file on the Ansible control node, substitutes variables and facts, and writes the resulting text to a managed host. A practical template workflow is therefore: create a .j2 file, provide its data through playbook or inventory variables, render it with src and dest, inspect the change, and then apply it.
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This guide shows the complete workflow for playbooks and roles, including conditionals, loops, facts, filters, Windows behavior, whitespace control, the difference between the template module and template lookup, and checks to perform when upgrading ansible-core.
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What an Ansible template does
Ansible uses Jinja2 templating to make dynamic expressions and access variables and facts. The template file remains ordinary text for the target application, while expressions such as {{ app_port }} are replaced during a run. Rendering occurs on the control node before the task is sent to the managed machine; the managed machine receives the rendered result rather than the original Jinja2 source.
A template is normally a UTF-8 file with a .j2 suffix. The suffix is a convention, not a requirement, but it makes the file’s purpose obvious to people and tooling. Keep the target application’s literal syntax unchanged and add Jinja2 only where output must vary.
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- Literal text: configuration keys, comments, and punctuation required by the target program.
- Expressions:
{{ variable_name }}inserts a value. - Statements:
{% if %}and{% for %}control which lines are emitted. - Comments:
{# explanation for the template author #}are removed from the rendered output.
Both the template file and any data read by the template module must be UTF-8 encoded. If a source file uses another encoding, convert it before running Ansible instead of trying to diagnose the resulting parser or character errors on the target host.
Minimal working example
Create this layout next to your playbook:
site.yml
templates/
app.conf.j2Define a variable and render the template with the fully qualified module name:
---
- name: Deploy application configuration
hosts: all
vars:
app_port: 8080
tasks:
- name: Render application configuration
ansible.builtin.template:
src: app.conf.j2
dest: /etc/myapp/app.conf
mode: '0644'The corresponding templates/app.conf.j2 file can be:
port={{ app_port }}
host={{ ansible_facts['hostname'] }}
{% if inventory_hostname in groups['webservers'] %}
role=web
{% else %}
role=other
{% endif %}With app_port set to 8080, Ansible gathers the current host name, evaluates the group membership test, and writes a normal text file such as port=8080, the host name, and either role=web or role=other. The official Ansible pattern uses this same combination of a templates directory, a .j2 file, the template module, src, dest, and a hostname fact.
Build a template step by step
1. Define the output contract
Start with the exact file the managed service expects: a service configuration, environment file, hosts file, or another text format. Write a static version first. This gives you a reference for required keys, quoting, indentation, separators, and trailing newlines before you introduce Jinja2.
2. Create the file in the correct templates directory
For a playbook, place the file in a templates/ directory associated with the playbook. For a role, place it in that role’s templates/ directory. The task’s src names the template relative to the location Ansible searches; do not point src at a file that exists only on the managed host.
Save the file as UTF-8. Keep the .j2 suffix unless a target application or an established project convention requires another name.
3. Supply the input data
Template values may come from several normal Ansible sources:
- Playbook variables: values under
varsfor a small, local example. - Inventory and group variables: host-specific or group-specific settings.
- Included variable files: data maintained separately from the playbook.
- Registered results: output captured from an earlier task.
- Command-line variables: values supplied with
-efor a deployment-specific override.
Use variable names made from letters, numbers, and underscores. Avoid names that collide with Ansible or Jinja2 internals, and prefer descriptive names such as app_port or tls_certificate_path over one-letter names.
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4. Insert scalar and structured values
Use double curly braces for interpolation:
port={{ app_port }}
log_level={{ app_log_level }}Nested dictionaries and facts can use bracket notation:
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address={{ ansible_facts['eth0']['ipv4']['address'] }}Dot notation can be convenient for simple keys, but bracket notation makes the key boundaries explicit and works well when a key contains characters that are not valid in a dotted expression. Ensure the fact or dictionary key exists for every host that will render the file. If a network interface is not consistently named, use a variable or a fact structure that is stable in your environment rather than hard-coding one interface name.
Filters transform a value to the syntax required by the destination. For example:
settings={{ application_settings | to_json }}
metadata:
{{ service_metadata | to_yaml }}Choose a filter based on the target parser. JSON embedded in a JSON file, YAML embedded in a YAML file, or an unquoted value in an INI-style file each has different escaping requirements.
5. Put variation in Jinja2 statements
Use {% if %} when a line or block should appear only for some hosts:
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{% endif %}Use {% for %} for repeated output:
allowed_user={{ item }}
{% for item in allowed_users %}
allowed_user={{ item }}
{% endfor %}Keep indentation and blank lines intentional. Many target formats treat whitespace as significant, and even formats that ignore spaces can be difficult to review when templates emit accidental blank lines.
6. Add the template task
Use the fully qualified collection name:
- name: Render service configuration
ansible.builtin.template:
src: service.conf.j2
dest: /etc/example/service.conf
mode: '0644'The FQCN avoids ambiguity if another collection provides a module with a similar short name. The module is designed to generate text files; it is not a general-purpose serializer for native Python or Jinja2 data types.
7. Preview and apply
Run a syntax check first, then use check and diff mode where the target and module support it:
ansible-playbook --syntax-check site.yml
ansible-playbook --check --diff site.yml
ansible-playbook site.ymlCheck mode and diff mode are operational safeguards: they let you inspect the rendered text and the proposed file change before making it. Review diffs for secrets, unintended whitespace, missing variables, and changes outside the lines you expected.
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Playbook templates versus role templates
Playbook-level organization
A playbook-level templates/ directory is useful when one playbook owns a small set of configuration files. The minimal example uses this arrangement. Keep the playbook and its templates together so a reader can find the source without searching a role collection.
Role-level organization
Reusable roles should put template files under the role’s templates/ directory and invoke them from tasks in that role:
roles/
web_config/
defaults/
main.yml
tasks/
main.yml
templates/
app.conf.j2# roles/web_config/tasks/main.yml
- name: Render application configuration
ansible.builtin.template:
src: app.conf.j2
dest: /etc/myapp/app.conf
mode: '0644'Role defaults provide safe values that callers can override with inventory, group variables, included data, or extra variables. Keep the role’s template and the task that renders it together; this makes the reuse boundary clear and prevents a role from depending on an unrelated playbook directory.
How variables reach a template
The template does not fetch inventory or command-line data by itself. Ansible assembles the variable context for the host, and Jinja2 evaluates expressions against that context while rendering. A practical mapping looks like this:
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| Data source | Typical use | Template expression |
|---|---|---|
Playbook vars |
A value used by one play or a compact example | {{ app_port }} |
| Inventory or group variables | Different settings for environments or host groups | {{ api_backend }} |
| Included variable file | Separating larger or environment-specific data sets | {{ database.host }} |
| Registered task result | Rendering information discovered earlier in the run | {{ command_result.stdout }} |
Extra variables with -e |
Per-run overrides and deployment parameters | {{ release_id }} |
| Ansible facts | Host properties gathered at the start of a play | {{ ansible_facts['hostname'] }} |
If a play disables fact gathering, fact expressions such as ansible_facts['hostname'] will not be available unless you gather or define the needed data another way. Treat missing data as a template input problem: verify the variable name, its scope, and whether the host actually receives the variable source you intended.
Conditionals, loops, and host-specific output
Conditional sections
Conditionals are best for optional directives, platform-specific settings, and role- or group-specific lines. Include the complete line inside the conditional so the output cannot contain a key with an empty value accidentally:
{% if inventory_hostname in groups['webservers'] %}
role=web
{% else %}
role=other
{% endif %}Repeated sections
Loops turn a list or dictionary into repeated text. A firewall template, for example, might emit one rule per host:
{% for host in groups['appservers'] %}
allow_host={{ host }} address={{ hostvars[host]['ansible_facts']['default_ipv4']['address'] }}
{% endfor %}Always confirm that the facts referenced for every loop item are gathered and have the same shape. A host without the expected address fact can make the whole rendering task fail.
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Ansible permits Jinja2 loops and conditionals in templates, but not as a substitute for YAML playbook structure. A template loop creates multiple lines in one output file; it does not create multiple Ansible tasks, retries, handlers, or remote commands. Use YAML task loops when each item needs its own module invocation, error handling, or notification, and use Jinja2 loops when the result is repeated text in one file.
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Template module behavior and useful options
The template module safely manages a destination file and can automatically decrypt Ansible Vault content used by the task. The rendered file is still text, so protect sensitive destinations with appropriate ownership and permissions in addition to encrypting source variables.
The most important parameters are:
src: the template source name, resolved on the control node.dest: the path of the rendered file on the managed host.mode: the destination permission mode, written as a quoted string such as'0644'to avoid YAML interpretation surprises.
Make sure the destination’s parent directory exists or create it in a preceding task. If a service needs to reload after a changed file, attach a handler to the template task rather than restarting it on every run.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Template module versus template lookup
Choose between the module and the lookup based on what you need to produce:
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ansible.builtin.template lookup |
|---|---|---|
| Output purpose | Renders text and writes a file to a managed host | Retrieves rendered content as a value for another task or expression |
| Data shape | Designed for text-file generation; native Jinja2 types are not used | Supports native-type behavior when templated content must remain a data structure |
| Typical location | A task that manages dest |
A variable assignment, argument, or other expression using lookup or query |
| Example | ansible.builtin.template: src: app.conf.j2 dest: /etc/myapp/app.conf |
lookup('ansible.builtin.template', 'fragment.j2') |
Use the module when the end result is a deployed text file. Use the lookup when a later task needs the rendered content itself, especially when native Jinja2 data types matter. The lookup supports lookup and query forms; verify the expected scalar or list shape before passing the result to another module.
Windows and newline behavior
For Windows targets, use ansible.windows.win_template rather than the POSIX-oriented template module. The Windows module defaults to CRLF newline sequences, which matches the normal Windows text convention. If a program requires a different newline style, set and test the appropriate option for that module and application.
Do not assume that a file rendered for Linux can be copied unchanged to Windows. Newline conventions, destination paths, permissions, and service reload mechanisms differ even when the Jinja2 expressions are identical.
Whitespace, delimiters, and files that contain Jinja-like text
Ansible has loaded templates with trim_blocks=True since Ansible 0.9. This removes the first newline after a block statement and can affect blank lines around {% if %} and {% for %}. Inspect the rendered diff when blank lines or indentation are significant.
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#jinja2: variable_start_string: '[[', variable_end_string: ']]', trim_blocks: False
message = [[ message_text ]]The header lets you preserve literal {{ and }} sequences required by another application while using alternate delimiters for the values Ansible must substitute. Keep the header as the first line and document the choice for future maintainers.
Validate a template before changing production files
- Check encoding: confirm that the template and included data are UTF-8.
- Check syntax: run
ansible-playbook --syntax-checkagainst the playbook. - Check variable availability: verify names, host scope, group membership, and fact gathering.
- Render in check mode: use
ansible-playbook --check --diffand read the rendered diff for every affected host. - Test representative hosts: include hosts from each group or platform branch used by your conditionals.
- Apply and verify: run the play, confirm the destination content and permissions, and let the service validate or reload the configuration.
Check mode is not a replacement for the target application’s own configuration validator. If the service provides a syntax-test command, run it in a separate validation task before notifying a reload handler.
Troubleshooting common failures
Undefined variable
An error naming a variable means the value was not in the rendering context for that host. Check spelling and scope, then confirm that the inventory group, included variable file, registered result, or -e argument is actually used by the play. If a value is optional, guard the complete block with an {% if %} test and choose an explicit default appropriate for the target application.
Template not found
Verify the path and spelling under the playbook’s or role’s templates/ directory. The src value is resolved on the control node, so creating a file only on the managed host does not fix this error.
Unexpected blank lines or indentation
Inspect block placement, the module’s trim_blocks=True behavior, and whether a loop emits a newline before or after each item. Use whitespace controls deliberately and preview with --diff instead of guessing from the source.
Wrong value type in a later task
The template module writes text and does not preserve native Jinja2 types. If a subsequent task needs a list, dictionary, Boolean, or number rather than serialized text, retrieve the rendered content with the template lookup and use its native-type behavior, or keep the data structure as a normal variable instead of serializing it into a file first.
Facts are missing
Fact expressions fail when fact gathering is disabled, a fact is unavailable on a platform, or the key differs between hosts. Gather the required facts, select a stable fact, or pass the needed value explicitly as inventory data.
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Rendered file works on one platform but not another
Check newline style, path syntax, permissions, and module choice. Windows targets generally require ansible.windows.win_template and its CRLF default; POSIX targets use the regular template module and POSIX file semantics.
Plan for ansible-core upgrades
Current ansible-core development documentation warns that version 2.19 introduced significant templating changes. Treat an ansible-core upgrade as a template compatibility change, not merely a controller package update.
- Record the ansible-core version used to render the current files.
- Run syntax checks, check mode, and diffs against representative inventories on the new version.
- Pay particular attention to whitespace, undefined values, native-type assumptions, and templates that rely on older delimiter behavior.
- Validate the resulting configuration with the target service before a broad rollout.
Keep the controller version, collections, and test inventory consistent in continuous integration so a templating change is detected before it reaches production.
Maintainable template patterns
- Keep business decisions in clearly named variables and use short, readable Jinja2 blocks in the file.
- Use filters such as
to_yamlandto_jsonat the boundary where data enters a format, rather than manually assembling escaped text. - Prefer role templates for reusable components and a playbook-level directory for one-off deployments.
- Use handlers for service reloads triggered by a changed template.
- Review rendered diffs for secrets and set restrictive destination permissions where needed.
- Document unusual delimiter headers and assumptions about facts, groups, and newline behavior.
- Keep task orchestration, retries, and per-item module calls in YAML; keep text generation logic in Jinja2.
With these boundaries, a template remains easy to test: variables describe the desired state, Jinja2 describes how that state becomes text, and the template task owns delivery of the rendered file.
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