How can I check if file has been downloaded in ans

问题:

I am downloading the file with wget from ansible.

  - name: Download Solr
    shell: chdir={{project_root}}/solr wget http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip

but I only want to do that if zip file does not exist in that location. Currently the system is downloading it every time.

回答1:

Unless you have a reason to use wget why not use get_url module. It will check if the file needs to be downloaded.

---
- hosts        : all
  gather_facts : no
  tasks:
   - get_url:
       url="http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip"
       dest="{{project_root}}/solr-4.7.0.zip"

NOTE: If you put the directory and not the full path in the dest ansible will still download the file to a temporary dir but do an md5 check to decide whether to copy to the dest dir.

And if you need to save state of download you can use:

---
- hosts        : all
  gather_facts : no
  tasks:
   - get_url:
       url="http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip"
       dest="{{project_root}}/solr-4.7.0.zip"
     register: get_solr

   - debug: 
       msg="solr was downloaded"
     when: get_solr|changed

回答2:

Note: this answer covers general question of "How can i check the file existence in ansible", not a specific case of downloading file.

The problems with the previous answers using "command" or "shell" actions is that they won't work in --check mode. Actually, first action will be skipped, and next will error out on "when: solr_exists.rc != 0" condition (due to variable not being defined).

Since Ansible 1.3, there's more direct way to check for file existance - using "stat" module. It of course also works well as "local_action" to check a local file existence:

- local_action: stat path={{secrets_dir}}/secrets.yml
  register: secrets_exist

- fail: msg="Production credentials not found"
  when: secrets_exist.stat.exists == False

回答3:

Many modules are already aware of the result and will be skipped if its already there, like file or geturl. Others like command have a creates option, which will skip this command if that file already exists (or doesn't exist, if you use the removes option).

So you should first check the available modules, if they are smart enough already. If not: I recommend the stats module. Advantage over the other solution: No "red errors but ignored" in the output.

- name: Check MySQL data directory existence
  stat: path=/var/lib/mysql-slave
  register: mysql_slave_data_dir

- name: Stop MySQL master to copy data directory
  service: name=mysql state=stopped
  sudo: yes 
  when: not mysql_slave_data_dir.stat.exists

回答4:

There are at least two options here.

You can register a variable if the file exists, then use a when condition to execute the command on the condition that the file doesn't already exist:

- command: /usr/bin/test -e {{project_root}}/solr/solr-4.7.0.zip
  register: solr_zip
  ignore_errors: True
- name: Download Solr
  shell: chdir={{project_root}}/solr /usr/bin/wget http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip
  when: solr_zip|failed

You could also use the commands module with the creates option:

- name: Download Solr
  command: /usr/bin/wget http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip chdir={{project_root}}/solr  creates={{project_root}}/solr/solr-4.7.0.zip

回答5:

So basically you can do this checking by registering a variable from a command and checking its return code. (You can also do this by checking its stdout)

- name: playbook
  hosts: all
  user: <your-user>

  vars:
    project_root: /usr/local

  tasks:

    - name: Check if the solr zip exists.
      command: /usr/bin/test -e {{project_root}}/solr/solr-4.7.0.zip
      ignore_errors: True
      register: solr_exists

    - name: Download Solr
      shell: chdir={{project_root}}/solr wget http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip
      when: solr_exists.rc != 0

This basically says that if the /usr/bin/test -e {{project_root}}/solr/solr-4.7.0.zip command returns a code that is not 0, meaning it doesn't exist then execute the task Download Solr

Hope it helps.

回答6:

This article might be useful

Out of it comes this example:

tasks:
  - shell: if [[ -f "/etc/monitrc" ]]; then /bin/true; else /bin/false; fi
    register: result
    ignore_errors: True

  - command: /bin/something
    when: result|failed

  - command: /bin/something_else
    when: result|success

  - command: /bin/still/something_else
    when: result|skipped

回答7:

Use the creates argument

- name: Download Solr
  shell: creates={{working_directory}}/solr/solr-4.7.0.zip chdir={{working_directory}}/solr wget http://mirror.mel.bkb.net.au/pub/apache/lucene/solr/4.7.0/solr-4.7.0.zip

回答8:

my favourite is to only download the file if it is newer than the local file (which includes when the local file does not exist)

the -N option with wget does this: https://www.gnu.org/software/wget/manual/html_node/Time_002dStamping-Usage.html .

sadly, i don't think there is an equivalent feature in get_url

so a very small change:

- name: Download Solr shell: chdir={{project_root}}/solr wget -N http://<SNIPPED>/solr-4.7.0.zip