[GitHub] [couchdb-documentation] nickva commented on a change in pull request #457: [RFC] Introduce CouchDB node types

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nickva commented on a change in pull request #457: [RFC] Introduce CouchDB node types
URL: https://github.com/apache/couchdb-documentation/pull/457#discussion_r348064337
 
 

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 File path: rfcs/013-node-types.md
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+---
+name: Node Types
+about: Introduce heterogeneous node types to CouchDB 4
+title: 'Node Types'
+labels: rfc, discussion
+assignees: ''
+
+---
+
+# Introduction
+
+This RFC proposes the ability to have different node types in CouchDB 4+. This
+would improve performance and allow for a more efficient use of resources.
+
+## Abstract
+
+Previously, in CouchDB 2 and 3, cluster functionality was uniformly distributed
+amongst the nodes. Any node could accept HTTP requests, run replication jobs
+and build secondary indices. With the FDB-based topology, CRUD operations have
+lower resource needs and so it could be useful to have a heterogeneous
+topology, where for example, CRUD operations run on lower capacity nodes, and a
+few higher capacity nodes handle replication or indexing jobs.
+
+
+## Requirements Language
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+"SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
+document are to be interpreted as described in
+[RFC 2119](https://www.rfc-editor.org/rfc/rfc2119.txt).
+
+## Terminology
+
+*node type* : A label used to designate a subset of CouchDB functionality.
+
+---
+
+# Detailed Description
+
+## Node Types
+
+A node type is a string description of a some internal CouchDB
+functionality. These are the initially defined node types:
+
+ * "api_frontend" : Indicates this node can accept HTTP API requests.
+ * "view_indexing" : Indicates this node can build map/reduce view indices.
+ * "search_indexing": Indicates this node can build search indices.
+ * "replication" : Indicates this node can run replication jobs.
+
+Users can configure CouchDB nodes with any combination of those types.
+
+## Configuration
+
+Configuration MAY be specified in the standard `.ini` files or via environment
+variables. Environment variables have a higher priority, and override the
+`.ini` based settings. By default, if not configured either via `.ini` files or
+environment variable, a node type is considered enabled i.e. the value defaults
+to `true`.
+
+### Configuration Files
+
+Configuration MUST be specified in the `[node_types]` section. Each type label,
+if specified, MUST be on a separate line and have a boolean value.
+
+Example:
+
+```
+[node_types]
+
+api_frontend = true
+view_indexing = false
+search_indexing = false
+replication = false
+
+```
+
+### Environment Variables
+
+Since in some cases it is easier to set environment variables than tweak `.ini`
+files, node types MAY be set via environment variables using the
+`COUCHDB_NODE_TYPE_` prefix. The prefix SHOULD be followed by the type label.
+If the value of the variable is `"false"` the functionality indicated will be
+disabled on that node. Any other value, indicates `true`.
+
+Example:
+
+`COUCHDB_NODE_TYPE_API_FRONTEND=false COUCHDB_NODE_TYPE_VIEW_INDEXING=true ...`
+
+## Implementation
+
+Implementation should be minimally invasive, at least for the node types listed
+above.
+
+ * `"api_frontend"` would disable `chttpd` application or its top supervisor.
+
+ * All background tasks in FDB are executed via the `couch_jobs` framework. The
+top level application supervisors typically have a separate `gen_server` in
+charge of accepting jobs and executing them. The implementation then would be
+as simple as having a `case` statement around the worker's `start_link()`
+function, such that if that background job type is `"false"`, that `gen_server`
+would return the `ignore` value to the supervisor.
+
+# Advantages and Disadvantages
+
+## Disadvantages
+
+ - More configuration-state complexity
+
+## Advantages
+
+ - Ability to utilize hardware resources better
+ - Possibly better security and isolation by running indexing and replication
+   jobs in an isolated environment inaccessible from the outside
+
+# Key Changes
+
+ - Heterogeneous node types
+ - New configuration section
+ - New configuration environment variables
+
+## Applications and Modules Affected
+
+ - chttpd
+ - fabric
+ - couch_views
 
 Review comment:
   Good call

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