Update design.md

docs/design/design.md

 # Deployment Manager Design
 
 ## Overview
-Deployment Manager is a service which can be run in a Kubernetes cluster that
+Deployment Manager is a service that runs in a Kubernetes cluster. It
 provides a declarative configuration language to describe Kubernetes
-resources and a mechanism for deploying, updating, and deleting configurations.
+resources, and a mechanism for deploying, updating, and deleting configurations.
 This document describes the configuration language, object model, and
 architecture of the service in detail.
 
@@ -41,8 +41,8 @@ resources:
 Resources can reference values from other resources. The version of Deployment
 Manager running in the Google Cloud Platform uses references to understand
 dependencies between resources and properly order the operations it performs on
-a configuration. (This version doesn't yet order operations to satisfy dependencies, 
-but it will soon.)
+a configuration. (This version of DM doesn't yet order operations to satisfy 
+dependencies, but it will soon.)
 
 A reference follows this syntax: **$(ref.NAME.PATH)**, where _NAME_ is the name
 of the resource being referenced, and _PATH_ is a JSON path to the value in the
@@ -58,6 +58,7 @@ In this case, _my-service_ is the name of the resource, and _metadata.name_ is
 the JSON path to the value being referenced.
 
 ### Configurable Resources
+
 Configurable resources are the primitive resources that can be configured in
 Deployment Manager, including:
 
@@ -67,17 +68,17 @@ Deployment Manager, including:
 
 Deployment Manager processes configurable resources by passing their
 configuration properties directly to kubectl on the cluster to create, update,
-or delete the resource.
+or delete the resources.
 
 ### Templates
 Templates are abstract types that can be created using Python or
-[Jinja](http://jinja.pocoo.org/). Templates take a set of properties and must
-output a valid YAML configuration string. Properties are bound to values when a
-template is instantiated in a configuration.
+[Jinja](http://jinja.pocoo.org/). A template takes a set of properties as input,
+and must output a valid YAML configuration string. Properties are bound to
+values when a template is instantiated in a configuration.
 
-Templates are expanded as a pre-processing step before configurable resources
+Templates are expanded in a pre-processing step before configurable resources
 are processed. They can output configurations containing configurable resources,
-or additional nested templates. Nested templates will be processed recursively.
+or additional nested templates. Nested templates are processed recursively.
 
 An example of a template in python is:
 
@@ -97,7 +98,7 @@ def GenerateConfig(context):
   return yaml.dump({'resources': resources})
 ```
 
-and in Jinja is:
+and in Jinja:
 
 ```
 resources:
@@ -108,22 +109,22 @@ resources:
     ...
 ```
 
-Templates provide access to several sets of data, which can be used for
-parameterizing or further customizing a configuration:
+Templates provide access to multiple sets of data, which can be used for
+parameterizing or further customizing configurations:
 
-* env: a map of values defined by Deployment Manager, including _deployment_,
-  _name_, and _type_
+* env: a map of key/value pairs from the environment, including pairs
+defined by Deployment Manager, such as _deployment_, _name_, and _type_
 * properties: a map of the key/value pairs passed in the properties section when
   instantiating the template
-* imports: a map of import file name to file contents of all imports originally
-  specified for the configuration
+* imports: a map of import file names to file contents of all imports
+originally specified for the configuration
 
 In Python, this data is available from the _context_ object passed into the
 _GenerateConfig_ method.
 
 ### Template Schemas
-A schema can be provided for a template. The schema describes the template in
-more details, including:
+A schema can be optionally provided for a template. The schema describes
+the template in more detail, including:
 
 * info: more information about the template, including long description and
   title
@@ -131,7 +132,7 @@ more details, including:
 * required: properties which are required when instantiating the template
 * properties: JSON Schema descriptions of each property the template accepts
 
-An example of a template schema is:
+Here's an example of a template schema:
 
 ```
 info:
@@ -151,19 +152,18 @@ properties:
     default: prop-value
 ```
 
-Schemas are used by Deployment Manager to validate properties being used during
-template instantiation and provide default value semantics on properties.
+Schemas are used by Deployment Manager to validate properties during
+template instantiation, and to provide default values.
 
-Schemas must be imported along-side the templates which they describe when
-passing configuration to Deployment Manager.
+Schemas must be imported with the templates they describe, when passing
+configuration to Deployment Manager.
 
 ### Instantiating Templates
-Templates can be instantiated in the same way that a configurable resource is
-used. They can be used in two different ways, either passed to the API as an
+Templates can be used in two different ways: either passed to the API as an
 imported file, or used from a public HTTP endpoint.
 
 #### Imported Templates
-Templates may be imported as part of the target configuration and used
+Templates can be imported as part of the target configuration, and used
 directly, for example:
 
 ```
@@ -177,15 +177,15 @@ resources:
     prop1: prop-value
 ```
 
-The _imports_ list is not understood by the Deployment Manager service, but is a
-directive to client-side tooling to specify what additional files should be
-included when passing a configuration to the API.
+The _imports_ list is not understood by the Deployment Manager service.
+It's a directive used by client-side tools to specify what additional files
+should be included when passing a configuration to the API.
 
 Using the Deployment Manager API, these templates can be included in the
-imports section of the _targetConfig_.
+imports section of the _configuration_.
 
 #### External Templates
-Templates may also be used from a public HTTP endpoint, for example:
+Templates can also be used from a public HTTP endpoint. For example:
 
 ```
 resources:
@@ -197,10 +197,10 @@ resources:
 
 The service will process external templates as follows:
 
-1. fetch the external template as an import
-1. attempt to fetch the schema for the template, using
-  _<full template path>.schema_ as the schema path
-1. repeat for any sub-imports found in the schema file
+1. Fetch the external template as an import
+1. Attempt to fetch the schema for the template, using
+_<full template path>.schema_ as the schema path
+1. Repeat for any sub-imports found in the schema file
 
 When fetching schema files and sub-imports, the base path of the external
 template is used for relative paths.
@@ -213,15 +213,15 @@ Deployments are the primary resource in the Deployment Manager service. The
 inputs to a deployment are:
 
 * name
-* targetConfig
+* configuration
 
-When creating a deployment, users pass their YAML configuration, as well as any
-import files (templates, datafiles, etc.) in as the _targetConfig_.
+When creating a deployment, users pass their configuration,
+as well as any import files (templates, datafiles, etc.), all encoded in `YAML`,
+in as the _configuration_.
 
-Creating, updating and deleting a deployment creates a new manifest for the
-deployment, and then processes the new configuration. In the case of deleting a
-deployment, the deployment is first updated to an empty manifest containing no
-resources, and then is removed from the system.
+Creating, updating or deleting a deployment creates a new manifest for the
+deployment. When deleting a deployment, the deployment is first updated to
+an empty manifest containing no resources, and then removed from the system.
 
 Deployments are available at the HTTP endpoint:
 
@@ -230,15 +230,12 @@ http://manager-service/deployments
 ```
 
 ### Manifests
-A manifest is created for a deployment every time it is mutated, including
-creation, update, and deletion.
-
-A manifest contains three major pieces of data:
+A manifest is created for a deployment every time it is changed. It contains
+three key components:
 
-* inputConfig: the original input configuration for the manifest, including YAML
-  configuration and imports
-* expandedConfig: the final expanded configuration to be used when processing
-  resources for the manifest
+* inputConfig: the original input configuration for the manifest
+* expandedConfig: the expanded configuration to be used when processing resources
+* for the manifest
 * layout: the hierarchical structure of the manifest
 
 Manifests are available at the HTTP endpoint:
@@ -248,6 +245,7 @@ http://manager-service/deployments/<deployment>/manifests
 ```
 
 #### Expanded Configuration
+
 Given a new _inputConfig_, Deployment Manager expands all template
 instantiations recursively until there is a flat set of configurable resources.
 This final set is stored as the _expandedConfig_ and is used during resource
@@ -321,53 +319,49 @@ in more detail below.
 
 Currently there are two caveats in the design of the service:
 
-* Synchronous API: the API is currently designed to block on all processing for
+* Synchronous API: the API currently blocks on all processing for
   a deployment request. In the future, this design will change to an
   asynchronous operation-based mode.
-* Non-persistence: the service currently stores all metadata in memory, so will
-  lose all knowledge of deployments and their metadata on restart. In the
-  future, the service will persist all deployment metadata in the cluster.
+* Non-persistence: the service currently stores all metadata in memory, 
+  so it will lose all knowledge of deployments and their metadata on restart.
+  In the future, the service will persist all deployment metadata.
 
 ### Manager
+
 The **manager** service acts as both the API server and the workflow engine for
-processing deployments. The process for a deployment is:
+processing deployments. It uses the following process:
 
 1. Create a new deployment with a manifest containing _inputConfig_ from the
    user request
-1. Call out to **expandybird** service to perform expansion on the _inputConfig_
+1. Call out to he **expandybird** service to expand the _inputConfig_
 1. Store the resulting _expandedConfig_ and _layout_
-1. Call out to **resourcifier** service to perform processing on resources from
-   the _expandedConfig_
+1. Call out to the **resourcifier** service to perform processing on resources
+from the _expandedConfig_
 1. Respond with success or error messages to the original API request
 
-The manager is responsible for all persistence of metadata associated with
+The manager is responsible for saving the metadata associated with
 deployments, manifests, type instances, and other resources in the Deployment
 Manager model.
 
 ### Expandybird
-The **expandybird** service takes in input configurations, including the YAML
-configuration and import files, performs all template expansion, and returns the
-resulting flat configuration and layout. It is completely stateless and handles
-requests synchronously.
 
-Because templates are Python or Jinja, the actual expansion process is performed
-in a sub-process running a Python interpreter. A new sub-process is created for
-every request to expandybird.
+The **expandybird** service takes in input configurations, performs all template
+expansions, and returns the resulting flat configuration and layout. It is completely
+stateless.
 
-Currently expansion is not sandboxed, but the intention of templates is to be
-reproducable hermetically sealed entities, so future designs may
-introduce a sandbox to limit external interaction like network and disk access
-during expansion.
+Because templates are written in Python or Jinja, the actual expansion process
+is performed in a sub-process that runs a Python interpreter. A new sub-process
+is created for every request to expandybird.
+
+Currently, expansion is not sandboxed, but templates should be reproducable,
+hermetically sealed entities. Future designs may therefore, introduce a sandbox to
+limit external interaction, such as  network or disk access, during expansion.
 
 ### Resourcifier
+
 The **resourcifier** service takes in flat expanded configurations containing
 only configurable resources, and makes the respective kubectl calls to process
-each resource. It is completely stateless and handles requests synchronously.
-
-Processing may be to create, update, or delete a resource,
-depending on the request. The resourcifier handles references, and is the major
-workflow engine for resource processing. In the future. it will also handle
-dependencies between resources, as described earlier.
+each resource. It is totally stateless, and handles requests synchronously.
 
-The resourcifier service returns either success or error messages encountered
-during resource processing.
+The resourcifier returns either success or error messages encountered during
+resource processing.