Using Lookups

Lookup plugins allow access of data in Ansible from outside sources. These plugins are evaluated on the Ansible control machine, and can include reading the filesystem but also contacting external datastores and services. These values are then made available using the standard templating system in Ansible, and are typically used to load variables or templates with information from those systems.

注解

This is considered an advanced feature, and many users will probably not rely on these features.

注解

Lookups occur on the local computer, not on the remote computer.

注解

Lookups are executed with a cwd relative to the role or play, as opposed to local tasks which are executed with the cwd of the executed script.

注解

Since 1.9 you can pass wantlist=True to lookups to use in jinja2 template “for” loops.

Intro to Lookups: Getting File Contents

The file lookup is the most basic lookup type.

Contents can be read off the filesystem as follows:

- hosts: all
  vars:
     contents: "{{ lookup('file', '/etc/foo.txt') }}"

  tasks:

     - debug: msg="the value of foo.txt is {{ contents }}"

The Password Lookup

注解

A great alternative to the password lookup plugin, if you don’t need to generate random passwords on a per-host basis, would be to use Vault. Read the documentation there and consider using it first, it will be more desirable for most applications.

password generates a random plaintext password and stores it in a file at a given filepath.

(Docs about crypted save modes are pending)

If the file exists previously, it will retrieve its contents, behaving just like with_file. Usage of variables like “{{ inventory_hostname }}” in the filepath can be used to set up random passwords per host (what simplifies password management in ‘host_vars’ variables).

Generated passwords contain a random mix of upper and lowercase ASCII letters, the numbers 0-9 and punctuation (”. , : - _”). The default length of a generated password is 20 characters. This length can be changed by passing an extra parameter:

---
- hosts: all

  tasks:

    # create a mysql user with a random password:
    - mysql_user: name={{ client }}
                  password="{{ lookup('password', 'credentials/' + client + '/' + tier + '/' + role + '/mysqlpassword length=15') }}"
                  priv={{ client }}_{{ tier }}_{{ role }}.*:ALL

    (...)

注解

If the file already exists, no data will be written to it. If the file has contents, those contents will be read in as the password. Empty files cause the password to return as an empty string

Starting in version 1.4, password accepts a “chars” parameter to allow defining a custom character set in the generated passwords. It accepts comma separated list of names that are either string module attributes (ascii_letters,digits, etc) or are used literally:

---
- hosts: all

  tasks:

    # create a mysql user with a random password using only ascii letters:
    - mysql_user: name={{ client }}
                  password="{{ lookup('password', '/tmp/passwordfile chars=ascii_letters') }}"
                  priv={{ client }}_{{ tier }}_{{ role }}.*:ALL

    # create a mysql user with a random password using only digits:
    - mysql_user: name={{ client }}
                  password="{{ lookup('password', '/tmp/passwordfile chars=digits') }}"
                  priv={{ client }}_{{ tier }}_{{ role }}.*:ALL

    # create a mysql user with a random password using many different char sets:
    - mysql_user: name={{ client }}
                  password="{{ lookup('password', '/tmp/passwordfile chars=ascii_letters,digits,hexdigits,punctuation') }}"
                  priv={{ client }}_{{ tier }}_{{ role }}.*:ALL

    (...)

To enter comma use two commas ‘,,’ somewhere - preferably at the end. Quotes and double quotes are not supported.

The CSV File Lookup

1.5 新版功能.

The csvfile lookup reads the contents of a file in CSV (comma-separated value) format. The lookup looks for the row where the first column matches keyname, and returns the value in the second column, unless a different column is specified.

The example below shows the contents of a CSV file named elements.csv with information about the periodic table of elements:

Symbol,Atomic Number,Atomic Mass
H,1,1.008
He,2,4.0026
Li,3,6.94
Be,4,9.012
B,5,10.81

We can use the csvfile plugin to look up the atomic number or atomic of Lithium by its symbol:

- debug: msg="The atomic number of Lithium is {{ lookup('csvfile', 'Li file=elements.csv delimiter=,') }}"
- debug: msg="The atomic mass of Lithium is {{ lookup('csvfile', 'Li file=elements.csv delimiter=, col=2') }}"

The csvfile lookup supports several arguments. The format for passing arguments is:

lookup('csvfile', 'key arg1=val1 arg2=val2 ...')

The first value in the argument is the key, which must be an entry that appears exactly once in column 0 (the first column, 0-indexed) of the table. All other arguments are optional.

Field Default Description
file ansible.csv Name of the file to load
delimiter TAB Delimiter used by CSV file. As a special case, tab can be specified as either TAB or t.
col 1 The column to output, indexed by 0
default empty string return value if the key is not in the csv file

注解

The default delimiter is TAB, not comma.

The INI File Lookup

2.0 新版功能.

The ini lookup reads the contents of a file in INI format (key1=value1). This plugin retrieve the value on the right side after the equal sign (‘=’) of a given section ([section]). You can also read a property file which - in this case - does not contain section.

Here’s a simple example of an INI file with user/password configuration:

[production]
# My production information
user=robert
pass=somerandompassword

[integration]
# My integration information
user=gertrude
pass=anotherpassword

We can use the ini plugin to lookup user configuration:

- debug: msg="User in integration is {{ lookup('ini', 'user section=integration file=users.ini') }}"
- debug: msg="User in production  is {{ lookup('ini', 'user section=production  file=users.ini') }}"

Another example for this plugin is for looking for a value on java properties. Here’s a simple properties we’ll take as an example:

user.name=robert
user.pass=somerandompassword

You can retrieve the user.name field with the following lookup:

- debug: msg="user.name is {{ lookup('ini', 'user.name type=properties file=user.properties') }}"

The ini lookup supports several arguments like the csv plugin. The format for passing arguments is:

lookup('ini', 'key [type=<properties|ini>] [section=section] [file=file.ini] [re=true] [default=<defaultvalue>]')

The first value in the argument is the key, which must be an entry that appears exactly once on keys. All other arguments are optional.

Field Default Description
type ini Type of the file. Can be ini or properties (for java properties).
file ansible.ini Name of the file to load
section global Default section where to lookup for key.
re False The key is a regexp.
default empty string return value if the key is not in the ini file

注解

In java properties files, there’s no need to specify a section.

The Credstash Lookup

2.0 新版功能.

Credstash is a small utility for managing secrets using AWS’s KMS and DynamoDB: https://github.com/LuminalOSS/credstash

First, you need to store your secrets with credstash:

$ credstash put my-github-password secure123

my-github-password has been stored

Example usage:

---
- name: "Test credstash lookup plugin -- get my github password"
  debug: msg="Credstash lookup! {{ lookup('credstash', 'my-github-password') }}"

You can specify regions or tables to fetch secrets from:

---
- name: "Test credstash lookup plugin -- get my other password from us-west-1"
  debug: msg="Credstash lookup! {{ lookup('credstash', 'my-other-password', region='us-west-1') }}"


- name: "Test credstash lookup plugin -- get the company's github password"
  debug: msg="Credstash lookup! {{ lookup('credstash', 'company-github-password', table='company-passwords') }}"

If you’re not using 2.0 yet, you can do something similar with the credstash tool and the pipe lookup (see below):

debug: msg="Poor man's credstash lookup! {{ lookup('pipe', 'credstash -r us-west-1 get my-other-password') }}"

The DNS Lookup (dig)

1.9.0 新版功能.

警告

This lookup depends on the dnspython library.

The dig lookup runs queries against DNS servers to retrieve DNS records for a specific name (FQDN - fully qualified domain name). It is possible to lookup any DNS record in this manner.

There is a couple of different syntaxes that can be used to specify what record should be retrieved, and for which name. It is also possible to explicitly specify the DNS server(s) to use for lookups.

In its simplest form, the dig lookup plugin can be used to retrieve an IPv4 address (DNS A record) associated with FQDN:

注解

If you need to obtain the AAAA record (IPv6 address), you must specify the record type explicitly. Syntax for specifying the record type is described below.

注解

The trailing dot in most of the examples listed is purely optional, but is specified for completeness/correctness sake.

- debug: msg="The IPv4 address for example.com. is {{ lookup('dig', 'example.com.')}}"

In addition to (default) A record, it is also possible to specify a different record type that should be queried. This can be done by either passing-in additional parameter of format qtype=TYPE to the dig lookup, or by appending /TYPE to the FQDN being queried. For example:

- debug: msg="The TXT record for gmail.com. is {{ lookup('dig', 'gmail.com.', 'qtype=TXT') }}"
- debug: msg="The TXT record for gmail.com. is {{ lookup('dig', 'gmail.com./TXT') }}"

If multiple values are associated with the requested record, the results will be returned as a comma-separated list. In such cases you may want to pass option wantlist=True to the plugin, which will result in the record values being returned as a list over which you can iterate later on:

- debug: msg="One of the MX records for gmail.com. is {{ item }}"
  with_items: "{{ lookup('dig', 'gmail.com./MX', wantlist=True) }}"

In case of reverse DNS lookups (PTR records), you can also use a convenience syntax of format IP_ADDRESS/PTR. The following three lines would produce the same output:

- debug: msg="Reverse DNS for 8.8.8.8 is {{ lookup('dig', '8.8.8.8/PTR') }}"
- debug: msg="Reverse DNS for 8.8.8.8 is {{ lookup('dig', '8.8.8.8.in-addr.arpa./PTR') }}"
- debug: msg="Reverse DNS for 8.8.8.8 is {{ lookup('dig', '8.8.8.8.in-addr.arpa.', 'qtype=PTR') }}"

By default, the lookup will rely on system-wide configured DNS servers for performing the query. It is also possible to explicitly specify DNS servers to query using the @DNS_SERVER_1,DNS_SERVER_2,...,DNS_SERVER_N notation. This needs to be passed-in as an additional parameter to the lookup. For example:

- debug: msg="Querying 8.8.8.8 for IPv4 address for example.com. produces {{ lookup('dig', 'example.com', '@8.8.8.8') }}"

In some cases the DNS records may hold a more complex data structure, or it may be useful to obtain the results in a form of a dictionary for future processing. The dig lookup supports parsing of a number of such records, with the result being returned as a dictionary. This way it is possible to easily access such nested data. This return format can be requested by passing-in the flat=0 option to the lookup. For example:

- debug: msg="XMPP service for gmail.com. is available at {{ item.target }} on port {{ item.port }}"
  with_items: "{{ lookup('dig', '_xmpp-server._tcp.gmail.com./SRV', 'flat=0', wantlist=True) }}"

Take note that due to the way Ansible lookups work, you must pass the wantlist=True argument to the lookup, otherwise Ansible will report errors.

Currently the dictionary results are supported for the following records:

注解

ALL is not a record per-se, merely the listed fields are available for any record results you retrieve in the form of a dictionary.

Record Fields
ALL owner, ttl, type
A address
AAAA address
CNAME target
DNAME target
DLV algorithm, digest_type, key_tag, digest
DNSKEY flags, algorithm, protocol, key
DS algorithm, digest_type, key_tag, digest
HINFO cpu, os
LOC latitude, longitude, altitude, size, horizontal_precision, vertical_precision
MX preference, exchange
NAPTR order, preference, flags, service, regexp, replacement
NS target
NSEC3PARAM algorithm, flags, iterations, salt
PTR target
RP mbox, txt
SOA mname, rname, serial, refresh, retry, expire, minimum
SPF strings
SRV priority, weight, port, target
SSHFP algorithm, fp_type, fingerprint
TLSA usage, selector, mtype, cert
TXT strings

More Lookups

Various lookup plugins allow additional ways to iterate over data. In Loops you will learn how to use them to walk over collections of numerous types. However, they can also be used to pull in data from remote sources, such as shell commands or even key value stores. This section will cover lookup plugins in this capacity.

Here are some examples:

---
- hosts: all

  tasks:

     - debug: msg="{{ lookup('env','HOME') }} is an environment variable"

     - debug: msg="{{ item }} is a line from the result of this command"
       with_lines:
         - cat /etc/motd

     - debug: msg="{{ lookup('pipe','date') }} is the raw result of running this command"

     # redis_kv lookup requires the Python redis package
     - debug: msg="{{ lookup('redis_kv', 'redis://localhost:6379,somekey') }} is value in Redis for somekey"

     # dnstxt lookup requires the Python dnspython package
     - debug: msg="{{ lookup('dnstxt', 'example.com') }} is a DNS TXT record for example.com"

     - debug: msg="{{ lookup('template', './some_template.j2') }} is a value from evaluation of this template"

     # loading a json file from a template as a string
     - debug: msg="{{ lookup('template', './some_json.json.j2', convert_data=False) }} is a value from evaluation of this template"


     - debug: msg="{{ lookup('etcd', 'foo') }} is a value from a locally running etcd"

     # shelvefile lookup retrieves a string value corresponding to a key inside a Python shelve file
     - debug: msg="{{ lookup('shelvefile', 'file=path_to_some_shelve_file.db key=key_to_retrieve') }}

     # The following lookups were added in 1.9
     - debug: msg="{{item}}"
       with_url:
            - 'https://github.com/gremlin.keys'

     # outputs the cartesian product of the supplied lists
     - debug: msg="{{item}}"
       with_cartesian:
            - list1
            - list2
            - list3

As an alternative you can also assign lookup plugins to variables or use them elsewhere. This macros are evaluated each time they are used in a task (or template):

vars:
  motd_value: "{{ lookup('file', '/etc/motd') }}"

tasks:

  - debug: msg="motd value is {{ motd_value }}"

参见

Playbooks
An introduction to playbooks
Conditionals
Conditional statements in playbooks
Variables
All about variables
Loops
Looping in playbooks
User Mailing List
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