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Exploring Ansible Variables Precedence with hash_behavior = merge A series of experiments was perfomed by defining overlapping dicts in the following files. The integer is to verify that the item was loaded regardless of precedence. Files are given relative to the root ansible-project directory with slashes replaced by spaces.
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| td: | |
| b: deploy_vars/all | |
| c: deploy_vars/all | |
| d: deploy_vars/all | |
| e: deploy_vars/all | |
| f: deploy_vars/all | |
| 2: deploy_vars/all |
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| According to the ansible docs | |
| http://docs.ansible.com/playbooks_variables.html#variable-precedence-where-should-i-put-a-variable | |
| The precedence should be | |
| * -e variables always win (yes) | |
| * then comes "most everything else" | |
| * then comes variables defined in inventory (not tested - hosts vars) | |
| * then comes facts discovered about a system (not tested - gather_facts ) | |
| * then "role defaults", which are the most "defaulty" and lose in priority to everything. (no) | |
| Summary | |
| Merge works in general with extra_vars. | |
| For variables in the ansible hierarchy | |
| merge only works within two closely tied pairs | |
| 1. roles/defaults/main.yml and roles/vars/main.yml | |
| 2. vars found in group_vars or loaded by a vars_plugin | |
| Discovered precedence | |
| most | |
| 1. extra vars | |
| --------- | |
| | 2. roles/x/defaults/main.yml | |
| | 3. roles/x/vars/main.yml | |
| --------- | |
| 4. site.yml defined in the vars: section of a play | |
| 5. site.yml defined in a vars: section upstream of the play | |
| -------- | |
| | 6. group_vars | |
| | 7. deploy_vars (folder depth increases precedence) | |
| -------- | |
| 8. vars/Debian.yml where Debian.yml is loaded by a vars_files: in site.yml interpolating on ansible_os_family | |
| 9. set_fact: in the task where debug: is called | |
| least |
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| comment out | |
| none | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {u'six': u'extra_vars.yml', 'e': 'roles/ubuntu_common/vars/main.yml', 5: 'ubuntu_common/defaults/main.yml', 'g': u'extra_vars.yml', 'f': u'extra_vars.yml', 'i': u'extra_vars.yml', 'h': u'extra_vars.yml', 'k': 'site_task.yml', u'j': u'extra_vars.yml', 7: 'site_task.yml', 4: 'roles/ubuntu_common/vars/main.yml', 'd': 'roles/ubuntu_common/vars/main.yml'}" | |
| } | |
| comment out | |
| extra_vars.yml | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'e': 'roles/ubuntu_common/vars/main.yml', 5: 'ubuntu_common/defaults/main.yml', 'g': 'roles/ubuntu_common/vars/main.yml', 'f': 'roles/ubuntu_common/vars/main.yml', 'i': 'site_task.yml', 'h': 'roles/ubuntu_common/vars/main.yml', 'k': 'site_task.yml', 'j': 'site_task.yml', 7: 'site_task.yml', 4: 'roles/ubuntu_common/vars/main.yml', 'd': 'roles/ubuntu_common/vars/main.yml'}" | |
| } | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'g': 'site_task.yml', 7: 'site_task.yml', 'i': 'site_task.yml', 'h': 'site_task.yml', 'k': 'site_task.yml', 'j': 'site_task.yml'}" | |
| } | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml, site.yml (site_task only) | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'g': 'site_upstream.yml', 8: 'site_upstream.yml', 'h': 'site_upstream.yml', 'k': 'site_upstream.yml', 'j': 'site_upstream.yml', 'i': 'site_upstream.yml'}" | |
| } | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml, site.yml | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'a': 'group_vars/all', 1: 'group_vars/all', 'c': 'deploy_vars/all', 'b': 'deploy_vars/all', 'e': 'deploy_vars/all', 'd': 'deploy_vars/all', 'f': 'deploy_vars/all', 'm': 'bridgepoint/vagrant.yml', 'k': 'bridgepoint/vagrant.yml', 11: 'bridgepoint/vagrant.yml', 12: 'bridgepoint.yml', 2: 'deploy_vars/all', 'o': 'bridgepoint/vagrant.yml', 'l': 'bridgepoint/vagrant.yml', 'p': 'bridgepoint.yml', 'n': 'bridgepoint/vagrant.yml'}" | |
| } | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml, site.yml | |
| group_vars and all deploy_vars tree | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'c': 'vars/Debian.yml', 3: 'vars/Debian.yml', 'e': 'vars/Debian.yml', 'd': 'vars/Debian.yml', 'g': 'vars/Debian.yml', 'f': 'vars/Debian.yml'}" | |
| } | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml, site.yml | |
| group_vars and all deploy_vars tree, vars/Debian.yml | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'i': 'task.yml', 9: 'task.yml', 'k': 'task.yml', 'j': 'task.yml', 'm': 'task.yml', 'l': 'task.yml'}" | |
| } | |
| --------------------- NOTE ON DEBUGING ------------ | |
| the debug statement expands msg="td {{td}}" for some variables | |
| TASK: [ubuntu_common | debug msg="td {u'six': u'extra_vars.yml', 4: 'roles/ubuntu_common/vars/main.yml', 'd': 'roles/ubuntu_common/vars/main.yml', 'g': u'extra_vars.yml', 7: 'site_task.yml', 'i': u'extra_vars.yml', 'h': u'extra_vars.yml', 'k': 'site_task.yml', u'f': u'extra_vars.yml', 'j': u'extra_vars.yml', 'e': 'roles/ubuntu_common/vars/main.yml'}"] *** | |
| <192.168.10.2> ESTABLISH CONNECTION FOR USER: vagrant | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {u'six': u'extra_vars.yml', 'e': 'roles/ubuntu_common/vars/main.yml', 5: 'ubuntu_common/defaults/main.yml', 'g': u'extra_vars.yml', 'f': u'extra_vars.yml', 'i': u'extra_vars.yml', 'h': u'extra_vars.yml', 'k': 'site_task.yml', u'j': u'extra_vars.yml', 7: 'site_task.yml', 4: 'roles/ubuntu_common/vars/main.yml', 'd': 'roles/ubuntu_common/vars/main.yml'}" | |
| } | |
| But it stops expanding the debug statement in the TASK: line here | |
| comment out extra_vars.yml, defaults/main.yml, vars/main.yml, site.yml (site_task only) | |
| TASK: [ubuntu_common | debug msg="td {{td}}"] ********************************* | |
| <192.168.10.2> ESTABLISH CONNECTION FOR USER: vagrant | |
| ok: [default] => { | |
| "item": "", | |
| "msg": "td {'g': 'site_upstream.yml', 8: 'site_upstream.yml', 'h': 'site_upstream.yml', 'k': 'site_upstream.yml', 'j': 'site_upstream.yml', 'i': 'site_upstream.yml'}" | |
| } |
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| append the following data structure with commandline arg --extra_vars "@extra_vars.yml" | |
| where extra_vars contains | |
| td: | |
| f: extra_vars.yml | |
| g: extra_vars.yml | |
| h: extra_vars.yml | |
| i: extra_vars.yml | |
| j: extra_vars.yml | |
| 6: extra_vars.yml |
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| td: | |
| a: group_vars/all | |
| b: group_vars/all | |
| c: group_vars/all | |
| d: group_vars/all | |
| e: group_vars/all | |
| 1: group_vars/all |
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| - set_fact: | |
| td: | |
| i: task.yml | |
| j: task.yml | |
| k: task.yml | |
| l: task.yml | |
| m: task.yml | |
| 9: task.yml |
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| td: | |
| d: roles/ubuntu_common/vars/main.yml | |
| e: roles/ubuntu_common/vars/main.yml | |
| f: roles/ubuntu_common/vars/main.yml | |
| g: roles/ubuntu_common/vars/main.yml | |
| h: roles/ubuntu_common/vars/main.yml | |
| 4: roles/ubuntu_common/vars/main.yml |
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| td: | |
| e: ubuntu_common/defaults/main.yml | |
| f: ubuntu_common/defaults/main.yml | |
| g: ubuntu_common/defaults/main.yml | |
| h: ubuntu_common/defaults/main.yml | |
| i: ubuntu_common/defaults/main.yml | |
| 5: ubuntu_common/defaults/main.yml |
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| td: | |
| c: vars/Debian.yml | |
| d: vars/Debian.yml | |
| e: vars/Debian.yml | |
| f: vars/Debian.yml | |
| g: vars/Debian.yml | |
| 3: vars/Debian.yml |
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The output shows that even with hash_behaviour = merge set in .ansible.cfg the overlapping dicts are merged only in rare cases. Most often, the dicts get clobbered by the highest precedence, perhaps merging with another dict at a similar precedence level (eg. roles/x/defaults/main.yml and roles/x/vars/main.yml)
After each run the dominant contributor is determined from debug output, and the dominant source is commented out for the next run.
Ansible has very basic merge hash behavior test here
https://github.com/ansible/ansible/blob/devel/test/integration/roles/test_hash_behavior/tasks/main.yml
and four test_variable_precedence roles here
https://github.com/ansible/ansible/tree/devel/test/integration/roles
But neither use the canonical ansible tree structure with all the possible places for variables.