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Document new PIPE_ONCE macro

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Lorin Hochstein 2013-02-17 12:47:51 -05:00
parent cd32597af0
commit ec16b854a5
1 changed files with 18 additions and 6 deletions
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24
docsite/rst/playbooks2.rst
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@ -125,9 +125,9 @@ For example::
{% endfor %} {% endfor %}
A frequently used idiom is walking a group to find all IP addresses in that group:: A frequently used idiom is walking a group to find all IP addresses in that group::
{% for host in groups['app_servers'] %} {% for host in groups['app_servers'] %}
{{ hostvars[host]['ansible_eth0']['ipv4']['address'] }} {{ hostvars[host]['ansible_eth0']['ipv4']['address'] }}
{% endfor %} {% endfor %}
An example of this could include pointing a frontend proxy server to all of the app servers, setting up the correct firewall rules between servers, etc. An example of this could include pointing a frontend proxy server to all of the app servers, setting up the correct firewall rules between servers, etc.
@ -137,7 +137,7 @@ Just a few other 'magic' variables are available... There aren't many.
Additionally, *inventory_hostname* is the name of the hostname as configured in Ansible's inventory host file. This can Additionally, *inventory_hostname* is the name of the hostname as configured in Ansible's inventory host file. This can
be useful for when you don't want to rely on the discovered hostname `ansible_hostname` or for other mysterious be useful for when you don't want to rely on the discovered hostname `ansible_hostname` or for other mysterious
reasons. If you have a long FQDN, *inventory_hostname_short* also contains the part up to the first reasons. If you have a long FQDN, *inventory_hostname_short* also contains the part up to the first
period, without the rest of the domain. period, without the rest of the domain.
Don't worry about any of this unless you think you need it. You'll know when you do. Don't worry about any of this unless you think you need it. You'll know when you do.
@ -469,7 +469,7 @@ be used like this::
# copy each file over that matches the given pattern # copy each file over that matches the given pattern
- action: copy src=$item dest=/etc/fooapp/ owner=root mode=600 - action: copy src=$item dest=/etc/fooapp/ owner=root mode=600
with_fileglob: with_fileglob:
- /playbooks/files/fooapp/* - /playbooks/files/fooapp/*
'with_file' loads data in from a file directly:: 'with_file' loads data in from a file directly::
@ -494,7 +494,7 @@ Many new lookup abilities were added in 0.9. Remeber lookup plugins are run on
tasks: tasks:
- action: debug msg="$item is an environment variable" - action: debug msg="$item is an environment variable"
with_env: with_env:
- HOME - HOME
- LANG - LANG
@ -536,7 +536,7 @@ can specify a start, end, and an optional step value.
Arguments can be either key-value pairs or as a shortcut in the format Arguments can be either key-value pairs or as a shortcut in the format
"[start-]end[/stride][:format]". The format is a printf style string. "[start-]end[/stride][:format]". The format is a printf style string.
Numerical values can be specified in decimal, hexadecimal (0x3f8) or octal (0600). Numerical values can be specified in decimal, hexadecimal (0x3f8) or octal (0600).
Negative numbers are not supported. This works as follows:: Negative numbers are not supported. This works as follows::
--- ---
@ -583,6 +583,18 @@ is an example using the authorized_key module, which requires the actual text of
The "$PIPE" macro works just like file, except you would feed it a command string instead. It executes locally, not remotely, as does $FILE. The "$PIPE" macro works just like file, except you would feed it a command string instead. It executes locally, not remotely, as does $FILE.
Because Ansible uses lazy evaluation, a "$PIPE" macro will be executed each time it is used. For
example, it will be executed separately for each host, and if it is used in a variable definition,
it will be executed each time the variable is evaluated.
The "$PIPE_ONCE" macro is an alternative that uses a caching strategy: it is executed only once, and
subsequent accesses use the cached value. One use case is for computing a timestamp that is intended
to be the same across all tasks and hosts that use it::
vars:
timestamp: $PIPE_ONCE(date +%Y%m%d-%H%M%S)
Selecting Files And Templates Based On Variables Selecting Files And Templates Based On Variables
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