Delegate a task to a different host on the remote machine?

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1

Hi All,

I am running a playbook that connects to remote host A, and would like to know if it is possible to run a delegate_to: command on the remote host A. The use case is that I have two different types of environments, one that relies on /etc/hosts to resolve the domain, and another type of environment that uses DNS to resolve the domain. So if I run delegate_to: “my.host.com”, it will either resolve to 127.0.0.1 in the case of a single instance, or it will resolve the public IP address in the case for a remote machine.

  • name: start all three mongodb services
    delegate_to: “{{ item.host }}”
    shell: creates=/var/lock/subsys/mongod-{{ item.name }} /etc/init.d/mongod-{{ item.name }} start
    with_flattened:
  • replication_servers

Any help would be appreciated

2

" am running a playbook that connects to remote host A, and would like to know if it is possible to run a delegate_to: command on the remote host A."

The delegate_to keyword is there to supply a different host to run on than one being traversed by Ansible’s host loop. If you are looping over the playbook on A, and want to run the command on A, you would leave off the delegate_to entirely.

I’m perhaps not understanding the question though.

3

Hi Michael, thank you for taking the time to respond!

It’s a bit of an unusual use case, so I am trying to understand if there is a better way to solve the problem.

I am setting up mongo replication on two types of environments

  1. Single-instance with replication for testing purposes
  2. Multi-instance with replication for production purposes
    In the single-instance case there are three init scripts on one machine
  • /etc/init.d/mongod-mongo1
  • /etc/init.d/mongod-mongo2
  • /etc/init.d/mongod-mongo3

Starting all three services on instance A is a simple task for the single instance topology

`

  • name: start all three mongodb service
    shell: creates=/var/lock/subsys/mongod-{{ item.name }} /etc/init.d/mongod-{{ item.name }} start

with_items:

`

However, if we’re dealing with a multi-instance topology, I would want to start /etc/init.d/mongo1 on instance A, and /etc/init.d/mongo2 on instance B, and /etc/init.d/mongo3 on instance C. Here is a a crappy solution to help illustrate the problem.

`

  • name: start all three mongodb service
    shell: ssh root@“{{ item.host}}”; creates=/var/lock/subsys/mongod-{{ item.name }} /etc/init.d/mongod-{{ item.name }} start
    with_items:
  • { name: mongo1, host: mongo1.example.com }
  • { name: mongo2, host: mongo2.example.com }
  • { name: mongo3, host: mongo3.example.com }

`

Thanks, Mike.

4

I'd do this without delegation, but with roles. I'd have one role that's parameterized with "instance name" , and have it applied 3 times to one host in testing and once (parameterized with host vars) per host in production.

Or even better, parameterize the role with list of mongo instances - then you'd be able to use the same play for tests and production.

Mike Trienis <mike.trienis@orcsol.com> napisał:

Hi Michael, thank you for taking the time to respond!

It's a bit of an unusual use case, so I am trying to understand if
there is
a better way to solve the problem.

I am setting up mongo replication on two types of environments

  1. Single-instance with replication for testing purposes
  2. Multi-instance with replication for production purposes

In the single-instance case there are three init scripts on one machine

  - /etc/init.d/mongod-mongo1
  - /etc/init.d/mongod-mongo2
  - /etc/init.d/mongod-mongo3

Starting all three services on instance A is a simple task for the
single
instance topology

- name: start all three mongodb service
shell: creates=/var/lock/subsys/mongod-{{ item.name }}
/etc/init.d/mongod-{{ item.name }} start
with_items:
   - { name: mongo1, host: mongo1.example.com }
   - { name: mongo2, host: mongo2.example.com }
   - { name: mongo3, host: mongo3.example.com }

This would be just:

- service: name={{ item.name }} state=started
  with_items: mongo_instances

With something like:
mongo_instances:
- name: mongo1
- name: mongo2
- name: mongo3

In the test host's variables

However, if we're dealing with a multi-instance topology, I would want
to
start */etc/init.d/mongo1* on instance A, and */etc/init.d/mongo2* on
instance B, and */etc/init.d/mongo3* on instance C. Here is a a crappy
solution to help illustrate the problem.

- name: start all three mongodb service
shell: ssh root@"{{ item.host}}"; creates=/var/lock/subsys/mongod-{{
item.name }} /etc/init.d/mongod-{{ item.name }} start
with_items:
   - { name: mongo1, host: mongo1.example.com }
   - { name: mongo2, host: mongo2.example.com }
   - { name: mongo3, host: mongo3.example.com }

For this you'd have to set the right instances in the right host's variables - the playbook could stay the same