Ansible normally has defaults that make sure to check the return codes of commands and modules and it fails fast – forcing an error to be dealt with unless you decide otherwise.
Sometimes a command that returns different than 0 isn’t an error. Sometimes a command might not always need to report that it ‘changed’ the remote system. This section describes how to change the default behavior of Ansible for certain tasks so output and error handling behavior is as desired.
Generally playbooks will stop executing any more steps on a host that has a task fail. Sometimes, though, you want to continue on. To do so, write a task that looks like this:
- name: this will not be counted as a failure command: /bin/false ignore_errors: yes
Note that the above system only governs the return value of failure of the particular task, so if you have an undefined variable used or a syntax error, it will still raise an error that users will need to address. Note that this will not prevent failures on connection or execution issues. This feature only works when the task must be able to run and return a value of ‘failed’.
New in version 2.2.
Connection failures set hosts as ‘UNREACHABLE’, which will remove them from the list of active hosts for the run. To recover from these issues you can use meta: clear_host_errors to have all currently flagged hosts reactivated, so subsequent tasks can try to use them again.
When a task fails on a host, handlers which were previously notified will not be run on that host. This can lead to cases where an unrelated failure can leave a host in an unexpected state. For example, a task could update a configuration file and notify a handler to restart some service. If a task later on in the same play fails, the service will not be restarted despite the configuration change.
You can change this behavior with the
--force-handlers command-line option,
or by including
force_handlers: True in a play, or
force_handlers = True
in ansible.cfg. When handlers are forced, they will run when notified even
if a task fails on that host. (Note that certain errors could still prevent
the handler from running, such as a host becoming unreachable.)
Ansible lets you define what “failure” means in each task using the
failed_when conditional. As with all conditionals in Ansible, lists of multiple
failed_when conditions are joined with an implicit
and, meaning the task only fails when all conditions are met. If you want to trigger a failure when any of the conditions is met, you must define the conditions in a string with an explicit
You may check for failure by searching for a word or phrase in the output of a command:
- name: Fail task when the command error output prints FAILED command: /usr/bin/example-command -x -y -z register: command_result failed_when: "'FAILED' in command_result.stderr"
or based on the return code:
- name: Fail task when both files are identical raw: diff foo/file1 bar/file2 register: diff_cmd failed_when: diff_cmd.rc == 0 or diff_cmd.rc >= 2
In previous version of Ansible, this can still be accomplished as follows:
- name: this command prints FAILED when it fails command: /usr/bin/example-command -x -y -z register: command_result ignore_errors: True - name: fail the play if the previous command did not succeed fail: msg: "the command failed" when: "'FAILED' in command_result.stderr"
You can also combine multiple conditions for failure. This task will fail if both conditions are true:
- name: Check if a file exists in temp and fail task if it does command: ls /tmp/this_should_not_be_here register: result failed_when: - result.rc == 0 - '"No such" not in result.stdout'
If you want the task to fail when only one condition is satisfied, change the
failed_when definition to:
failed_when: result.rc == 0 or "No such" not in result.stdout
If you have too many conditions to fit neatly into one line, you can split it into a multi-line yaml value with
- name: example of many failed_when conditions with OR shell: "./myBinary" register: ret failed_when: > ("No such file or directory" in ret.stdout) or (ret.stderr != '') or (ret.rc == 10)
When a shell/command or other module runs it will typically report “changed” status based on whether it thinks it affected machine state.
Sometimes you will know, based on the return code or output that it did not make any changes, and wish to override the “changed” result such that it does not appear in report output or does not cause handlers to fire:
tasks: - shell: /usr/bin/billybass --mode="take me to the river" register: bass_result changed_when: "bass_result.rc != 2" # this will never report 'changed' status - shell: wall 'beep' changed_when: False
You can also combine multiple conditions to override “changed” result:
- command: /bin/fake_command register: result ignore_errors: True changed_when: - '"ERROR" in result.stderr' - result.rc == 2
Sometimes it’s desirable to abort the entire play on failure, not just skip remaining tasks for a host.
any_errors_fatal play option will end the play when any tasks results in an error and stop execution of the play:
- hosts: somehosts any_errors_fatal: true roles: - myrole
for finer-grained control
max_fail_percentage can be used to abort the run after a given percentage of hosts has failed.
Most of what you can apply to a single task (with the exception of loops) can be applied at the Blocks level, which also makes it much easier to set data or directives common to the tasks. Blocks also introduce the ability to handle errors in a way similar to exceptions in most programming languages. Blocks only deal with ‘failed’ status of a task. A bad task definition or an unreachable host are not ‘rescuable’ errors:
tasks: - name: Handle the error block: - debug: msg: 'I execute normally' - name: i force a failure command: /bin/false - debug: msg: 'I never execute, due to the above task failing, :-(' rescue: - debug: msg: 'I caught an error, can do stuff here to fix it, :-)'
This will ‘revert’ the failed status of the outer
block task for the run and the play will continue as if it had succeeded.
See Blocks error handling for more examples.