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Ansible 1.3 Conditional Execution -- Very complete example with comments -- I find the conditional expressions to be ridiculously hard to get right in Ansible. I don't have a good model of what's going on under the surface so I often get it wrong. What makes it even harder is that there has been at least three different variants over the course …
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# This has been tested with ansible 1.3 with these commands:
# ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts isFirstRun=false"
# ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts isFirstRun=true"
# ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts"
# NB: The type of the variable is crucial!
- name: Ansible Conditionals Examples
hosts: $hosts
vars_files:
- vars.yml
tasks:
########### Correct COMPLEX expressions ###################
# Need parentheses around $is_live, because it (may) contain an _or_, and _and_ has higher prio than _or_;
- name: ($is_live) and (isFirstRun == 'true') # OK only if isFirstRun is defined.
command: echo hello
when: ($is_live) and (isFirstRun == 'true')
# isFirstRun is a string var, whereas is_mgmt is an expression evaluating to a string, so it seems we need the $ to dereference it
- name: $is_mgmt and (isFirstRun == 'true') # OK only if isFirstRun is defined
command: echo hello
when: $is_mgmt and (isFirstRun == 'true')
- name: $is_mgmt and (isFirstRun != 'false') # OK only if isFirstRun is defined
command: echo hello
when: $is_mgmt and (isFirstRun != 'false')
- name: $is_mgmt and (not isFirstRun == 'false') # OK only if isFirstRun is defined
command: echo hello
when: $is_mgmt and (not isFirstRun == 'false')
########### SIMPLE expressions ############################
- name: is_mgmt # OK
command: echo hello
when: is_mgmt
- name: $is_mgmt # OK
command: echo hello
when: $is_mgmt
- name: ($is_mgmt) # OK
command: echo hello
when: ($is_mgmt)
- name: (is_mgmt) # WRONG - Always runs
command: echo hello
when: (is_mgmt)
######
- name: isFirstRun == 'true' # OK
command: echo hello
when: isFirstRun == 'true'
- name: not isFirstRun != 'true' # OK
command: echo hello
when: not isFirstRun != 'true'
- name: not isFirstRun == 'false' # OK
command: echo hello
when: not isFirstRun == 'false'
- name: isFirstRun != 'false' # OK
command: echo hello
when: isFirstRun != 'false'
- name: $isFirstRun == 'true' # WRONG - $isFirstRun is interpreted as true and true is not equal to 'true' so only works for negative match
command: echo hello
when: $isFirstRun == 'true'
########### All wrong #####################################
- name: ($is_live == True) and (isFirstRun == 'true') # WRONG - Only first live node on true (none of false (correct))
command: echo hello
when: ($is_live == True) and (isFirstRun == 'true')
- name: $is_live and (isFirstRun == 'true') # WRONG - Correct when true, but only first live when false
# ['$inventory_hostname' == 'tsrvuweblive71' or '$inventory_hostname' == 'tsrvuweblive72' and (isFirstRun == 'true')]
command: echo hello
when: $is_live and (isFirstRun == 'true')
- name: is_live and (isFirstRun == 'true') # WRONG - All nodes run on true (none of false (correct))
command: echo hello
when: is_live and (isFirstRun == 'true')
- name: ($is_live == 'True') and (isFirstRun == 'true') # WRONG - Only first live node on true (none on false (correct))
command: echo hello
when: ($is_live == 'True') and (isFirstRun == 'true')
- name: (is_live == 'True') and (isFirstRun == 'true') # WRONG - No nodes run on niether true nor false - is_live not dereferenced
command: echo hello
when: (is_live == 'True') and (isFirstRun == 'true')
######
- name: is_mgmt and (isFirstRun == 'true')
# WRONG - All run on true
command: echo hello
when: is_mgmt and (isFirstRun == 'true')
- name: is_mgmt and (isFirstRun != 'false')
# WRONG - All run on true
command: echo hello
when: is_mgmt and (isFirstRun != 'false')
- name: is_mgmt and (not isFirstRun == 'false')
# WRONG - All run on true
command: echo hello
when: is_mgmt and (not isFirstRun == 'false')
- name: mgmt and isFirstRun equal true with ()
# WRONG - Does not run when isFirstRun is 'false' (which is correct), but runs all nodes when 'true'
command: echo hello
when: ((is_mgmt) and (isFirstRun == 'true'))
- name: mgmt and isFirstRun not_equal true with $
# WRONG - Always runs mgmt irrespective of value of isFirstRun
command: echo hello
when: $is_mgmt and $isFirstRun != 'true'
- name: mgmt and not isFirstRun equal true with $
# # WRONG - Always runs mgmt irrespective of value of isFirstRun
command: echo hello
when: $is_mgmt and not $isFirstRun == 'true'
- name: mgmt and isFirstRun equal true with $
# WRONG - Never runs any node
command: echo hello
when: $is_mgmt and $isFirstRun == 'true'
- name: mgmt and not isFirstRun equal true with only_if and $
# WRONG - All nodes run
command: echo hello
only_if: "'$is_mgmt' and not '$isFirstRun' == 'true'"
- name: mgmt and isFirstRun not_equal true with only_if and $
# WRONG - All nodes run
command: echo hello
only_if: "'$is_mgmt' and '$isFirstRun' != 'true'"
- name: mgmt and isFirstRun not_equal true with ()
# WRONG - All nodes run when isFirstRun is false and no nodes run when isFirstRun is true
command: echo hello
when: ((is_mgmt) and (isFirstRun != 'true'))
- name: mgmt and isFirstRun not_equal true
# WRONG - All nodes run when isFirstRun is false and no nodes run when isFirstRun is true
command: echo hello
when: is_mgmt and isFirstRun != 'true'
- name: mgmt and not isFirstRun equal true
# WRONG - All nodes run when isFirstRun is false and no nodes run when isFirstRun is true
command: echo hello
when: is_mgmt and not isFirstRun == 'true'
- name: mgmt and not isFirstRun equal true with ()
# WRONG - All nodes run when isFirstRun is false and no nodes run when isFirstRun is true
command: echo hello
when: ((is_mgmt) and (not isFirstRun == 'true'))
- name: mgmt and not isFirstRun equal true with only_if, $ and ()
# ERROR Conditional expression must evaluate to True or False: ($is_mgmt) and (not '$isFirstRun' == 'true')
command: echo hello
only_if: "($is_mgmt) and (not '$isFirstRun' == 'true')"
---
# The "" makes this evaluate to a string. Which is good in some cases and bad in other...
is_mgmt: "'$inventory_hostname' == 'webmgmt'"
is_live: "'$inventory_hostname' == 'weblive1' or '$inventory_hostname' == 'weblive2'"
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