# How best to implement basic horizontal scaling?

**URL:** <https://forum.ansible.com/t/how-best-to-implement-basic-horizontal-scaling/12423>\
**Category:** Ansible Project\
**Tags:** ansible-project, ubuntu\
**Created:** [February 25, 2013, 8:12pm UTC](https://forum.ansible.com/t/how-best-to-implement-basic-horizontal-scaling/12423 "2013-02-25T20:12:10Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Michael\_DeHaan](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@Michael\_DeHaan](https://forum.ansible.com/u/Michael_DeHaan)\
**Post date:** [February 25, 2013, 8:12pm UTC](https://forum.ansible.com/t/how-best-to-implement-basic-horizontal-scaling/12423/1 "2013-02-25T20:12:10Z")

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> I'm writing a playbook as a learning exercise, with a narrow scope of  
> installing Gitorious and its dependencies on Ubuntu "Cloud" Precise amd64.  
> As part of the learning exercise, I wish to learn how best to do tiered  
> application playbooks.
> 
> Link to my Gitorious playbook repo:  
> [https://gitorious.org/apb-gitorious/apb-gitorious](https://gitorious.org/apb-gitorious/apb-gitorious)

We talked about this on IRC, but nice ...

> For example, I see Gitorious as entailing the following components:
> 
> a database for Gitorious (typically it's mysql, but I'm going to try  
> PostgreSQL)  
> SphinxSearch  
> a database for Gitorious (PostgreSQL again)  
> ActiveMQ  
> Gitorious + httpd + leftovers
> 
> While l honestly feel it inefficient to prematurely farm the five above  
> components out to separate machines (in my case it will be five m1.tiny  
> private OpenStack instances), my goal here is to learn how to assemble  
> tiered SaaS playbooks with parameters for horizontal scaling. As instances  
> are more granular, they are easier to load-balance in virtualization  
> environments. Other pros and cons occur to me about this sort of horizontal  
> scaling, but I suppose that is out of scope here. 🙂

Basically you would have a playbook that defined each layer in the  
system, that would include only the tasks needed on each.

This playbook would map those groups (i.e. control\_sever) to the tasks  
just the tier would perform.

The all in one playbook would just include more of the task and handler files.

The basic idiom I use is a "playbook maps groups of hosts to the roles  
that they perform or steps that need to be run on those hosts".

> Beyond the scaling out, I'd like the playbook I write for Gitorious to  
> easily scale back into an all-in-one install, for those who don't want or  
> need such scale. Installing OpenStack with Ansible is another target I have  
> in mind for this approach. In OpenStack there are many ways to assemble  
> such tiers.
> 
> At the moment, as an Ansible beginner, it seems best to define roles/tiers  
> for each component with a host group to bind them together. So, I'm  
> thinking instead of the "fooapp" or "webservers" in the best practices  
> example, I'd do roles: gitorious, sphinxsearch, postgresql, activemq. I'm  
> not sure how I'd handle two separate postgresql servers for the moment, but  
> my intent is to keep even those on discrete instances.

> Please me know what you think and thanks for your time.

Sounds exactly right to me, though there is clearly plenty of options  
of how to do it.