whacky idea for command DSL

mtl.dsl.markdown

MTL, Meta Tool Language

Preparation

Use mtl init to initialize the environment for mtl. Creates a workspace in current working directory.

mtl init 

Default values are: --name $(hostname) --dir $(pwd)

Initialize mtl with a specific name and base directory.

mtl init --name Targa.local --dir /home/alexh/mtl

Info

Return a metadata value by specifying the name of the property.

mtl info --name|-n <property>

Get the value of the name property.

mtl info --name name

returns ...

web1.local    

Get the value of the dir property.

mtl info -n dir

returns ...

/home/alexh/mtl

Attributes

Set and get attributes

Use mtl attribute to declare attributes about this instance. Can describe properties and state.

mtl attribute -n listen_port -v 8080
mtl attribute -n mypath      -v /my/path
mtl attribute -n status      -v active

Return the value of an attribute.

mtl attribute -n listen_port 

returns... 8080

Use a prefix in the attribute to organize them. Use machine-tags format.

mtl attribute -n namespace:predicate -v value   

Declare some attributes across several namespaces.

mtl attribute -n packages:tomcat      -v tomcat-7.0.42.zip
mtl attribute -n packages:estore      -v estore-1.0.42.war
mtl attribute -n estore:customer      -v acme.com
mtl attribute -n estore:url           -v http://192.168.50.12:8080/estore
mtl attribute -n tomcat:listen_port   -v 8080
mtl attribute -n tomcat:catalina_base -v /home/tomcat

Alternative mtl syntax using long option name for name and value parameters.

mtl attribute --name listen_port --value 8080

Use attributes to model metrics.

mtl attribute -n metrics:estore.deploys  -v 5
mtl attribute -n metrics:estore.restarts -v 5

Clear and remove attributes

mtl attribute --name|-n <attribute> [--clear --remove]

Clear the value for status.

mtl attribute -n status --clear

Remove status.

mtl attribute -n status --remove

List attributes

Use mtl attributes to list all the attributes for this instance.

mtl attributes

List attribute names in foo namespace.

mtl attributes -n "tomcat:*"

returns...

tomcat:listen_port
tomcat:catalina_base

List attributes and show their values.

mtl attributes -n "tomcat:*" --value

returns...

 tomcat:listen_port 8080
 tomcat:catalina_base /home/tomcat

Commands

Declare commands

Declare new commands with mtl command.

Define status command with an inline script:

mtl command -n status --script "curl -sf `mtl attribute -n estore:url`; exit $?"

A stop command that executes a script file:

mtl command -n stop --scriptfile $(mtl info -n dir)/bin/stop

Define stop command but scriptfile is a url address:

mtl command -n stop --scriptfile http://repo/script

Delegate command to another module. The other module must contain the same command.

mtl command -n start --delegate altmodule

List commands

List the commands with mtl commands.

mtl commands

returns ...

start
status
stop

List commands starting with 'sto':

mtl commands -n "sto*"

returns ...

stop

Execute commands

Use mtl exec to execute declared commands.

Execute start command defined in this instance:

mtl exec -n stop

Execute a command with options:

mtl exec -n status --url $(mtl attribute estore:url)

Execute a command in another mtl module

mtl exec -m othermodule -n command

Command options

Declare options for a command

Use mtl option to declare an option for a command.

mtl option -n <name> --command <> --arguments <> --default <> --description <>

Create an option called --jumps for the command, dance:

mtl option -n jumps --command dance --arguments true --default 3 --description 'num times to jump'

Changes usage for the dance command to:

mtl exec dance --jumps <3>

Similar usage as stubbs:add-option.

List options

Specify the command name:

mtl option --command dance

returns ...

jumps

Local metadata storage

Instance directory structure

The mtl init initializes a directory structure and stores metadata for the new mtl instance

.
|-- attributes/
|-- commands/
`-- metadata

The metadata file contains the name and dir values used by mtl init

name="Targa.local"
dir="/home/alexh/mtl
created_at="Thu Jan 16 09:20:56 PST 2014"
created_by="alexh"

The attributes and commands directory are discussed in sections below.

Attribute local storage

Attribute metadata stored in flat files

.
|-- attributes/
|   |-- listen_port/
|   |-- mypath/
|   `-- status/
|       `-- metadata
|-- commands/
`-- metadata

The metadata file contains the properties about the attribute

cat ./attributes/status/metadata
NAME="status"
VALUE="myvalue"

Command local storage

Command metadata stored in flat files

 .
 |-- attributes/
 |-- commands/
 |   |-- start/
 |   |-- status/
 |   `-- stop/
 |       `-- metadata
 `-- metadata

The metadata file contains the properties about the attribute

cat ./commands/stop/metadata
NAME="stop"
DESCRIPTION="stop command"
OPTIONS=""

Synchronization

mtl data can be shared with other nodes through synchronization of the mtl metadata. How synchronization is done depends on the backend.

Module containing backend implementation is defaulted to ... env_var or attribute?

publish

The publish flag synchronizes mtl state with the backend.

Publish a single attribute to a backing store

mtl attribute -n myvar --publish

Push all attributes matching pattern

mtl attributes -n "stuff:*" --publish

Push the commands

mtl commands --publish

refresh

The refresh flag retrieves the latest update from the backing store.

Refresh value for attribute myvar

mtl attribute -n myvar --refresh

Pull all the attributes

mtl attributes --refresh

Defaults

Adding mtl commands (syntax sugar)

A defaults system could store handlers for invoking user defined mtl commands.

Here a script handles calls to mtl defined commands.

mtl defaults handler --script "$(mtl exec ${1} ${2} ${@:3})"

Turns user defined commands into mtl sub commands.

mtl stop --foo bar

Default handler resolves to: mtl exec stop --foo bar

Don't like the word 'mtl'?

Alternative names to mtl.

meta.

meta attribute -n sayhi -v hi

meta command -n sayhi -script "echo ${1:-$(yo:attribute sayhi:message)}"  
meta exec sayhi --message "hello"  
meta sayhi --message "hello"

node.

node attribute sayhi hi

node command sayhi -script "echo ${1:-$(yo:attribute sayhi:message)}"  
node exec sayhi  "hello"  
node sayhi  "hello"

self.

self attribute sayhi:message hi
self attribute --name sayhi:message --value hi
self exec status

yo. Yo is self in spanish:

yo:attribute sayhi:message hi

yo:command sayhi -script "echo ${1:-$(yo:attribute sayhi:message)}"  
yo:exec sayhi  "hello"  
yo:sayhi  "hello"

proto. because it's a prototype object system design:

proto:attribute fooattry value_1 ;# alternative namespace ideas

object. object system:

object:attribute fooattry value_1  ;# ditto

instance. same as object:

instance:attribute fooattry value_1  ;# ditto

Scratch

mtl exec mtl command -n stop