具有静态清单的Ansible EC2

Question

I'm using ansible to provision servers on EC2, using the dynamic inventory and exact_count. This lets me scale up/down when I need to, which is nice.

Now I need to add a unique variable to the environment on each server when I provision them. One way I thought of doing this is using the inventory file like this:

[ec2-servers]
host1 myvar=abc
host2 myvar=def
...

where host1(2) somehow refer to the relevant EC2 instance, via tag_SomeName_host1 or similar.

But this doesn't tie in with how I'm currently provisioning servers. The dynamic inventory with exact_count gives me a set of identical clone servers.

Is there a way I can define servers in my inventory file, and have ansible provision it in ec2 if it doesn't exist, and remove it if a server exists in ec2 but not the inventory?

eg

I run my playbook for the first time with the inventory:

[ec2-servers]
host1 myvar=1

Then later I need to scale up so edit the inventory:

[ec2-servers]
host1 myvar=1
host2 myvar=2

and ansible ignores host1 as it already exists, then provisions an instance for host2.

Then later I no longer need the extra server so modify the inventory:

[ec2-servers]
host1 myvar=1

and ansible removes host2 from ec2.

Answer 1

No. Ansible doesn't [care to]:

• maintain the revision history of your inventory file
• compare every time there is a change
• execute playbooks/plays/tasks conditionally based on detected changes.

You need to build the logic yourself in the playbook.

Something like, my_playbook.yml :

- hosts: to_be_provisioned
  tasks:
  - include: provision_ec2_host.yml

- hosts: to_be_unprovisioned
  tasks:
  - include: unprovision_ec2_host.yml

both unprovision_ec2_host.yml & provision_ec2_host.yml should be idempotent of course.

Now you need to ensure that your inventory has correct set of hosts under the host-groups to_be_provisioned & to_be_unprovisioned and run my_playbook.yml.

$ cat inventory.ini
[to_be_provisioned]
host1 myvar=1

[to_be_unprovisioned]
host2 myvar=2

$ ansible-playbook -i inventory.ini my_playbook.yml
$ # modify inventory
$ cat inventory.ini
[to_be_provisioned]
host1 myvar=1
host2 myvar=2

# [to_be_unprovisioned] -- no hosts

$ ansible-playbook -i inventory.ini my_playbook.yml
$ # modify inventory
$ cat inventory.ini
[to_be_provisioned]
host1 myvar=1

[to_be_unprovisioned]
host2 myvar=2

$ ansible-playbook -i inventory.ini my_playbook.yml

Finally, to do this whole thing automatically, you can use your dynamic inventory . I recommend just make a copy of existing ec2.py and modify it so it returns the groups as you want.