[chef] Re: [chef-dev] Re: The future of the database and application cookbooks

["Jason J. W. Williams" < >]

I would agree with Alex. Trying to force MySQL, Redis and Riak (as examples) 
into the same generic DB cookbook abstraction will turn into a cookbook that 
in theory works universally, but in practice works well for no one, it seems 
to me. ...for the same reasons that trying to force a MySQL data 
model onto Riak will fail. These are fundamentally different systems, with 
only superficial similarities. 

-J

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On Aug 30, 2011, at 22:26, Alex Soto 
<
 >
 wrote:

> Thanks for the opportunity to discuss, always a good thing to hear 
> different opinions.
> 
> As an engineer I totally understand the desire to DRY up these common 
> patterns, but IMO these multi-stack/generic cookbooks add complexity to the 
> cookbook and pull in lots of dependencies I don't use, cluttering up my 
> cookbook repo.
> 
> I see this being similar to the 'rails' database agnosticism of the 
> migrations dsl.  I've only used it once, and that was due to engineering 
> curiosity of how well it worked using sqlite locally and a 'real' db in 
> production.  In practice, there has always been something that forced me to 
> go outside the dsl and run db specific DDL.  So in my experience you really 
> don't utilize this particular db agnosticism feature once you pick a stack, 
> but it adds lot's of engineering effort for the feature implementor to 
> cover all the variations in platforms.
> 
> With databases' in particular, each vendor has their peculiarities, so I 
> see lot's of rat holes in a single cookbook that covers different databases 
> and deployment patterns.  I understand that's the reason for providers, but 
> I think the engineering effort is better spent getting a kick-ass db 
> specific cookbook versus a superficial cookbook that kinda/sorta works 
> across db's.
> 
> Alex
> 
> 
> On Aug 30, 2011, at 7:39 PM, Noah Kantrowitz wrote:
> 
>> As some people have noticed from my musings on IRC and elsewhere, I have 
>> embarked on a (probably long overdue) overhaul of the application and 
>> database cookbooks. This is largely orthogonal (for now) with the recent 
>> LWRPs added to the database cookbook, though in the end they would be 
>> removed. What follows is a set of syntax ideas for where I think this 
>> should head. Not all of this is implemented, but you can see what is in my 
>> cookbooks branch https://github.com/coderanger/cookbooks/tree/COOK-634.
>> 
>> Database clusters
>> =================
>> 
>> In the new LWRP hierarchy the top level resource is a database_cluster. 
>> This defines an abstract model of a single-master-multi-slave cluster 
>> setup. Within a cluster is one or more database_servers, each of which 
>> defines a single type of database service (MySQL, Postgres, Redis, 
>> Cassandra, etc) mapped on to the containing cluster. In general I would 
>> expect most clusters to only contain a single database_server block, but 
>> this isn't required and if you have a beefy primary box for, say, both 
>> Postgres and Redis and wanted to have both use the same backup machine you 
>> could put those both in the same cluster definition. Within a 
>> database_server you can define database and users, though this isn't 
>> needed for all types of servers and the exact implementation of what those 
>> two constructs do is left up the backend plugin implementing the specified 
>> server type.
>> 
>> With all that laying down the model, lets look at some syntax:
>> 
>> database_cluster "prod"
>> master_role "prod_database_master"
>> slave_role "prod_database_slave"
>> 
>> database_server do
>>  type :mysql
>>  database "prod" do
>>    engine "innodb"
>>  end
>>  user "myuser" do
>>    password "xxx"
>>    grant do
>>      select "prod"
>>      insert "prod"
>>      update "prod"
>>    end
>>  end
>> end
>> 
>> database_server do
>>  type :redis
>> end
>> end
>> 
>> This will create a cluster running a MySQL server with one database named 
>> prod and a Redis server (in the case of Redis there are no specific tuning 
>> params we need to worry about so far). This example shows a very verbose 
>> form of the desired syntax, below is an equivalent version using some more 
>> sugar and allowing for sane defaults:
>> 
>> database_cluster "prod"
>> mysql do
>>  database do
>>    engine "innodb"
>>  end
>>  user "myuser" do
>>    password "xxx"
>>    grant "prod" do
>>      select
>>      insert
>>      update
>>    end
>>  end
>> end
>> 
>> redis
>> end
>> 
>> You can also pass Hashes to database and user instead of blocks if you 
>> want to feed them from an external data source (such as a data bag):
>> 
>> database_cluster "prod"
>> mysql do
>>  database "prod", {:engine => "innodb"}
>>  user "myuser", {:password => "xxx", :grant => {:select => "prod, ...}}
>> end
>> 
>> redis
>> end
>> 
>> As mentioned before, the actual implementation can choose how to handle 
>> databases and users. In the above examples, if you added any to the redis 
>> section it would simply be a no-op (or maybe a runtime error?). Also as a 
>> structural piece, database and user definitions will only ever be 
>> processed on the database master (are there databases where this isn't the 
>> case and slaves should create users and such too?). The individual 
>> backends for this would live in the cookbook for that program, so the 
>> database cookbook would only hold the core infrastructure and plumbing to 
>> run things. The idea is that this resource block would be placed somewhere 
>> central and assigned to all servers so they can use it for reference (see 
>> below in the app cookbook section). Only nodes with the master or slave 
>> role would actually do anything. As a special case if the system detects 
>> that the master role actually doesn't exist it will run in a degraded mode 
>> assuming a single-node cluster (so obviously the current node is the 
>> master).
>> 
>> The database cookbook would also grow an associated knife-database plugin 
>> to handle replication setup/teardown as for some databases you have to 
>> perform an out-of-band data sync before attaching the slave.
>> 
>> Seen in isolation, does this seem suitable flexible to cover most needs? I 
>> am mostly familiar with SQL databases and a few smaller NoSQL products, so 
>> for the greater NoSQL world is this still a viable model?
>> 
>> 
>> Application deployment
>> ======================
>> 
>> The model for the application LWRPs is generally simpler in terms of data, 
>> but is also more callback-driven. The top-level application resource just 
>> contains the central data used for all applications, and then any 
>> framework or platform specific bits are contained in sub-resources similar 
>> to the database_server arrangement. Below is an example of deploying the 
>> Radiant CMS:
>> 
>> application "radiant" do
>> path "/srv/radiant"
>> owner "nobody"
>> group "nogroup"
>> repository "git://github.com/radiant/radiant.git"
>> revision "master"
>> packages ["libxml2-dev", "libxslt1-dev", "libsqlite3-dev"]
>> migrate true
>> 
>> rails do 
>>  gems "bundler" => nil, "RedCloth" => "4.2.3"
>>  database :mysql => "radiant_production" do
>>    user "radiant"
>>    reconnect true
>>    encoding "utf8"
>>  end
>>  migration_command "bundle exec rake db:migrate"
>> end
>> 
>> unicorn do
>>  port 8000
>> end
>> end
>> 
>> The global data maps very directly to fields in the existing application 
>> data bags, except that they are not Hashes indexed by environment name. In 
>> the rails sub-resource you see that again things mostly map to the data 
>> bag. The biggest exception is the database section which doesn't actually 
>> state any information about the database. Instead things are looked up by 
>> reference to the information in the database resource. It would still be 
>> possible to specify all information manually if you aren't using the 
>> database cookbook.
>> 
>> Application backends define actions as callbacks more or less, to provide 
>> code to execute at different points during the deploy process. The current 
>> callbacks are :before_compile, :before_deploy, :before_migrate, 
>> :before_symlink, :before_restart, and :after_restart. The last 4 just map 
>> to the existing callbacks in the deploy resource system. before_compile 
>> takes place as the first thing when the application resource executes (so 
>> when the provider is compiled), while before_deploy takes place during the 
>> execute phase in the provider, but after the main application folder 
>> structure is created.
>> 
>> The plan is to convert all the existing application cookbook recipes into 
>> a small wrapper just piping data bags into this LWRP structure, so they 
>> should continue to work as they always have.
>> 
>> So, what do people think? Is this a step in the right direction for 
>> application deployment? Do you like the idea but what a different syntax 
>> for it? Are there big, glaring use cases I've missed?
>> 
>> --Noah Kantrowitz
>> 
>> 
>> 
>> tl;dr Application deployment with Chef is going to be awesome!
>> 
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