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Difference between revisions of "Trove/Replication-And-Clustering-With-Nodes"

(updated remove node notes and changed to DELETE)
Line 1: Line 1:
−
== Cassandra ==
+
== Summary ==
 +
<br>
 +
==== Summary of instance.cluster{} Fields for Instance-Create ====
 +
{| class="wikitable"
 +
|-
 +
! Field !! Type !! Description !! Applicable Datastore(s)
 +
|-
 +
| size || int || size of the new cluster || mongdb, cassandra, couchbase, redis-cluster
 +
|-
 +
| slave.of || string (uuid) || instance-id of the master of which to be a slave || mysql, redis, redis-cluster
 +
|-
 +
| slave.read_only || boolean || whether this slave should be read-only || mysql, redis, redis-cluster
 +
|}
 +
<br>
 +
<br>
 +
==== Summary of instance.cluster{} Fields for Instance-Show ====
 +
{| class="wikitable"
 +
|-
 +
! Field !! Type !! Description !! Datastore(s)
 +
|-
 +
| size || int || size of the cluster (excluding slaves) || mongdb, cassandra, couchbase, redis-cluster
 +
|-
 +
| nodes || array || instance-ids of nodes || mongdb, cassandra, couchbase, redis-cluster
 +
|-
 +
| slaves || array || instance-ids of slaves || mysql, redis, redis-cluster
 +
|-
 +
| slave.of || string (uuid) || instance-id of master (if a slave) || mysql, redis, redis-cluster
 +
|-
 +
| slave.read_only || boolean || if a slave, whether it's read-only || mysql, redis, redis-cluster
 +
|}
 +
<br>
 +
==== Summary of Route Changes ====
 +
<br>
 +
New Route:
 +
<pre>
 +
GET /instances/<id>/node/<node-id>
 +
</pre>
 +
<pre>
 +
{
 +
  "node": {
 +
    "status": "<status>",
 +
    "id": "<node-id>",
 +
    "name": "<name>",
 +
    "created": "<timestamp>",
 +
    "updated": "<timestamp>",
 +
    "links": [{...}],
 +
    "ip": ["<ip>"], //or hostname, depending on conf
 +
    "volume": {
 +
      "size": <size>,
 +
      "used": <used>
 +
    }
 +
  }
 +
}
 +
</pre>
 +
New Route:
 +
<pre>
 +
POST /instances/<id>/node/<node-id>/action
 +
</pre>
 +
<pre>
 +
{
 +
  "<action>": {
 +
    <action-specific fields>
 +
  }
 +
}
 +
</pre>
 +
<br>
 +
== Example: Cassandra ==
 +
<br>
 +
To illustrate the approach, Cassandra is used in the examples below. The eccentricities of each Datastore will be explained in their own sections.
 +
<br>
 
<br>
 
<br>
 
==== Create Instance ====
 
==== Create Instance ====
Line 12: Line 81:
 
     "datastore": {
 
     "datastore": {
 
       "type": "cassandra",
 
       "type": "cassandra",
−
       "version": "2.0.5"
+
       "version": "2.0.6"
 
     },
 
     },
 
     "configuration": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
 
     "configuration": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
Line 20: Line 89:
 
     },
 
     },
 
     "cluster": {
 
     "cluster": {
−
       "num_nodes": 3
+
       "size": 3
 
     }
 
     }
 
   }
 
   }
Line 39: Line 108:
 
     "datastore": {
 
     "datastore": {
 
       "type": "cassandra",
 
       "type": "cassandra",
−
       "version": "2.0.5"
+
       "version": "2.0.6"
 
     },
 
     },
 
     "configuration": {
 
     "configuration": {
Line 53: Line 122:
 
     },
 
     },
 
     "cluster": {
 
     "cluster": {
−
       "num_nodes": 3,
+
       "size": 3,
 
       "nodes": [
 
       "nodes": [
 
         {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
 
         {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
Line 66: Line 135:
 
Notes:
 
Notes:
 
* The instance.name now acts as the "cluster name", and in the case of Cassandra, the actual cluster_name.
 
* The instance.name now acts as the "cluster name", and in the case of Cassandra, the actual cluster_name.
−
* cluster.num_nodes indicates how many nodes should be in the initial cluster (required)
+
* cluster.size indicates how many nodes should be in the initial cluster (required)
 
* The cluster.nodes[].id are generated uuids
 
* The cluster.nodes[].id are generated uuids
 
* Cassandra-specific fields that are required to construct the initial cluster (num_tokens, endpoint_snitch, seed ip-list, etc.) are to be determined/calculated based on configuration file values and common-sense.
 
* Cassandra-specific fields that are required to construct the initial cluster (num_tokens, endpoint_snitch, seed ip-list, etc.) are to be determined/calculated based on configuration file values and common-sense.
Line 92: Line 161:
 
     "datastore": {
 
     "datastore": {
 
       "type": "cassandra",
 
       "type": "cassandra",
−
       "version": "2.0.5"
+
       "version": "2.0.6"
 
     },
 
     },
 
     "configuration": {
 
     "configuration": {
Line 106: Line 175:
 
     },
 
     },
 
     "cluster": {
 
     "cluster": {
−
       "num_nodes": 3,
+
       "size": 3,
 
       "nodes": [
 
       "nodes": [
 
         {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
 
         {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
Line 155: Line 224:
 
* the node.status will likely mirror the state values and transitions seen in instance.status prior to the clustering implementation.
 
* the node.status will likely mirror the state values and transitions seen in instance.status prior to the clustering implementation.
 
<br>
 
<br>
−
==== Modify Node ====
+
==== Scale Nodes ====
 
<br>
 
<br>
−
Example: Drain (http://www.datastax.com/documentation/cassandra/2.0/cassandra/tools/toolsDrain.html)
+
Request:
  
 
<pre>
 
<pre>
−
POST /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/node/416b0b16-ba55-4302-bbd3-ff566032e1c1/action
+
POST /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/action
 +
 
 
{
 
{
−
   "drain": {}
+
   "resize_cluster": {
 +
    "size": 6
 +
  }
 
}
 
}
 
</pre>
 
</pre>
 
<br>
 
<br>
−
==== Remove Node ====
+
Response:
 +
<pre>
 +
HTTP 202 (Empty Body)
 +
</pre>
 +
<br>
 +
Notes:
 +
* For the first iteration, only increasing the number of nodes is supported (decreasing is not).
 +
<br>
 +
==== All Other Operations ====
 +
<br>
 +
Notes:
 +
* Other operations like: removing a node, replacing a running node, replacing a dead node, repairing a node, etc. are not supported in the first iteration.
 +
<br>
 +
== Example: MySQL ==
 +
<br>
 +
==== Create Instance ====
 
<br>
 
<br>
 
Request:
 
Request:
  
 
<pre>
 
<pre>
−
DELETE /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/node/ff9d680c-fde3-49c6-a84e-76173b6df39d
+
POST /instances
 +
{
 +
  "instance": {
 +
    "name": "products",
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
 +
    "flavorRef": "7",
 +
    "volume": {
 +
      "size": 1
 +
    }
 +
  }
 +
}
 +
</pre>
 +
 
 +
Response:
 +
 
 +
<pre>
 +
{
 +
  "instance": {
 +
    "status": "BUILD",
 +
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
 +
    "name": "products",
 +
    "created": "2014-04-25T20:19:23",
 +
    "updated": "2014-04-25T20:19:23",
 +
    "links": [{...}],
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": {
 +
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
 +
      "links": [{...}],
 +
    },
 +
    "flavor": {
 +
      "id": "7",
 +
      "links": [{...}],
 +
    },
 +
    "volume": {
 +
      "size": 1
 +
    }
 +
  }
 +
}
 
</pre>
 
</pre>
 
<br>
 
<br>
−
Notes:
+
==== Create Slave ====
−
* "Remove" is specifically referring to http://www.datastax.com/documentation/cassandra/2.0/cassandra/operations/ops_remove_node_t.html
 
−
* Will likely have to add validation that a DELETE will not being the cluster into a bad state.
 
 
<br>
 
<br>
 +
Request:
 +
 +
<pre>
 +
POST /instances
 +
{
 +
  "instance": {
 +
    "name": "products-slave",
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": "fc318e00-3a6f-4f93-af99-146b44912188",
 +
    "flavorRef": "7",
 +
    "volume": {
 +
      "size": 1
 +
    },
 +
    "cluster": {
 +
      "slave": {
 +
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
 +
        "read_only": true
 +
      }
 +
    }
 +
  }
 +
}
 +
</pre>
  
−
==== Scale Up Nodes ====
+
Response:
 +
 
 +
<pre>
 +
{
 +
  "instance": {
 +
    "status": "BUILD",
 +
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
 +
    "name": "products",
 +
    "created": "2014-04-25T20:19:23",
 +
    "updated": "2014-04-25T20:19:23",
 +
    "links": [{...}],
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": {
 +
      "id": "fc318e00-3a6f-4f93-af99-146b44912188",
 +
      "links": [{...}],
 +
    },
 +
    "flavor": {
 +
      "id": "7",
 +
      "links": [{...}],
 +
    },
 +
    "volume": {
 +
      "size": 1
 +
    },
 +
    "cluster": {
 +
      "slave": {
 +
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
 +
        "read_only": true
 +
      }
 +
    }
 +
  }
 +
}
 +
</pre>
 +
<br>
 +
==== Show Master ====
 
<br>
 
<br>
 
Request:
 
Request:
  
 
<pre>
 
<pre>
−
POST /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/action
+
GET /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998
 +
</pre>
 +
 
 +
Response:
  
 +
<pre>
 
{
 
{
−
   "resize_cluster": {
+
   "instance": {
−
     "num_nodes": 6
+
     "status": "ACTIVE",
 +
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
 +
    "name": "products",
 +
    "created": "2014-04-25T20:19:23",
 +
    "updated": "2014-04-25T20:19:23",
 +
    "links": [{...}],
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": {
 +
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
 +
      "links": [{...}],
 +
    },
 +
    "flavor": {
 +
      "id": "7",
 +
      "links": [{...}],
 +
    },
 +
    "volume": {
 +
      "size": 1
 +
    },
 +
    "cluster": {
 +
      "slaves": [
 +
        {"id": "061aaf4c-3a57-411e-9df9-2d0f813db859"}
 +
      ]
 +
    }
 
   }
 
   }
 
}
 
}
 
</pre>
 
</pre>
 
<br>
 
<br>
 +
==== Show Slave ====
 +
<br>
 +
Request:
 +
 +
<pre>
 +
GET /instances/061aaf4c-3a57-411e-9df9-2d0f813db859
 +
</pre>
 +
 
Response:
 
Response:
 +
 
<pre>
 
<pre>
−
HTTP 202 (Empty Body)
+
{
 +
  "instance": {
 +
    "status": "ACTIVE",
 +
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
 +
    "name": "products",
 +
    "created": "2014-04-25T20:19:23",
 +
    "updated": "2014-04-25T20:19:23",
 +
    "links": [{...}],
 +
    "datastore": {
 +
      "type": "mysql",
 +
      "version": "5.5"
 +
    },
 +
    "configuration": {
 +
      "id": "fc318e00-3a6f-4f93-af99-146b44912188",
 +
      "links": [{...}],
 +
    },
 +
    "flavor": {
 +
      "id": "7",
 +
      "links": [{...}],
 +
    },
 +
    "volume": {
 +
      "size": 1
 +
    },
 +
    "cluster": {
 +
      "slave": {
 +
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
 +
        "read_only": true
 +
      }
 +
    }
 +
  }
 +
}
 
</pre>
 
</pre>
 
<br>
 
<br>
 +
== MongoDB ==
 +
<br>
 +
Notes:
 +
* instance.name will function as the replica-set name
 +
* The smallest viable deployment pattern for a replica-set is 3 nodes. A three member replica-set can either be (a) a primary and two secondaries or (b) a primary, a secondary, and an arbiter. option (b) provides less redundancy and fault tolerance, so it will not be supported in this first iteration. Therefore, size=3 by default creates a three member replica-set with one primary and two secondaries.
 +
* instance.cluster.size will only support '3', '5', and '7' as values for MongoDB in this first iteration. Why? (a) an odd number of members ensures the replica-set is always able to elect a primary (b) only 7 members can vote at a time.
 +
** Scaling the Nodes from 3 to 5, or 5 to 7 will be supported.
 +
** A replica-set can have up to 12 members, but only 7 voting members. To avoid having to implement and handle 'priority'/'hidden' in the first iteration, the maximum number of nodes is capped at 7.
 +
* Changing the priority, hidden, slaveDelay, or adding an Arbiter will not be supported in this first iteration.
 +
<br>
 +
== Couchbase ==
 +
<br>
 +
Notes:
 +
* instance.cluster.size can be any positive number
 +
* Scaling the Nodes by increasing the number will be supported.
 +
* Removing a Node will not be supported in the first iteration.

Revision as of 20:44, 28 April 2014

Summary


Summary of instance.cluster{} Fields for Instance-Create

Field Type Description Applicable Datastore(s)
size int size of the new cluster mongdb, cassandra, couchbase, redis-cluster
slave.of string (uuid) instance-id of the master of which to be a slave mysql, redis, redis-cluster
slave.read_only boolean whether this slave should be read-only mysql, redis, redis-cluster



Summary of instance.cluster{} Fields for Instance-Show

Field Type Description Datastore(s)
size int size of the cluster (excluding slaves) mongdb, cassandra, couchbase, redis-cluster
nodes array instance-ids of nodes mongdb, cassandra, couchbase, redis-cluster
slaves array instance-ids of slaves mysql, redis, redis-cluster
slave.of string (uuid) instance-id of master (if a slave) mysql, redis, redis-cluster
slave.read_only boolean if a slave, whether it's read-only mysql, redis, redis-cluster


Summary of Route Changes


New Route: 

GET /instances/<id>/node/<node-id>

{
  "node": {
    "status": "<status>",
    "id": "<node-id>",
    "name": "<name>",
    "created": "<timestamp>",
    "updated": "<timestamp>",
    "links": [{...}],
    "ip": ["<ip>"], //or hostname, depending on conf
    "volume": {
      "size": <size>,
      "used": <used>
    }
  }
}

New Route: 

POST /instances/<id>/node/<node-id>/action

{
  "<action>": {
    <action-specific fields>
  }
}


Example: Cassandra


To illustrate the approach, Cassandra is used in the examples below. The eccentricities of each Datastore will be explained in their own sections.

Create Instance


Request: 

POST /instances
{
  "instance": {
    "name": "products",
    "datastore": {
      "type": "cassandra",
      "version": "2.0.6"
    },
    "configuration": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
    "flavorRef": "7",
    "volume": {
      "size": 1
    },
    "cluster": {
      "size": 3
    }
  }
}

Response: 

{
  "instance": {
    "status": "BUILD",
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "cassandra",
      "version": "2.0.6"
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    },
    "cluster": {
      "size": 3,
      "nodes": [
        {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
        {"id": "7f52e4f9-3fa6-4238-ac08-1ce15197329a"},
        {"id": "ff9d680c-fde3-49c6-a84e-76173b6df39d"}
      ]
    }
  }
}


Notes:

  • The instance.name now acts as the "cluster name", and in the case of Cassandra, the actual cluster_name.
  • cluster.size indicates how many nodes should be in the initial cluster (required)
  • The cluster.nodes[].id are generated uuids
  • Cassandra-specific fields that are required to construct the initial cluster (num_tokens, endpoint_snitch, seed ip-list, etc.) are to be determined/calculated based on configuration file values and common-sense.


Show Instance


Request: 

GET /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998

Response: 

{
  "instance": {
    "status": "ACTIVE",
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "cassandra",
      "version": "2.0.6"
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    },
    "cluster": {
      "size": 3,
      "nodes": [
        {"id": "416b0b16-ba55-4302-bbd3-ff566032e1c1"},
        {"id": "7f52e4f9-3fa6-4238-ac08-1ce15197329a"},
        {"id": "ff9d680c-fde3-49c6-a84e-76173b6df39d"}
      ]
    }
  }
}


Notes:

  • Change: instance.volume.used, instance.ip[], and instance.hostname will never be returned
    • It's possible that instance.ip[] can remain if it only returns the seed ips.
    • It's possible that instance.hostname can remain if it's converted to an array and only contains the seed hostnames.
  • Change: the semantic meaning of instance.status, and the possible states, will change


Show Node


Request: 

GET /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/node/416b0b16-ba55-4302-bbd3-ff566032e1c1

Response: 

{
  "node": {
    "status": "ACTIVE",
    "id": "416b0b16-ba55-4302-bbd3-ff566032e1c1",
    "name": "products-1",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "ip": ["10.0.0.1"],
    "volume": {
      "size": 2,
      "used": 0.17
    }
  }
}


Notes:

  • node.name is the instance.name with "-<num>" as a suffix (counter for the cluster, starting at 1)
  • the node.status will likely mirror the state values and transitions seen in instance.status prior to the clustering implementation.


Scale Nodes


Request: 

POST /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/action

{
  "resize_cluster": {
    "size": 6
  }
}


Response: 

HTTP 202 (Empty Body)


Notes:

  • For the first iteration, only increasing the number of nodes is supported (decreasing is not).


All Other Operations


Notes:

  • Other operations like: removing a node, replacing a running node, replacing a dead node, repairing a node, etc. are not supported in the first iteration.


Example: MySQL


Create Instance


Request: 

POST /instances
{
  "instance": {
    "name": "products",
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
    "flavorRef": "7",
    "volume": {
      "size": 1
    }
  }
}

Response: 

{
  "instance": {
    "status": "BUILD",
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    }
  }
}


Create Slave


Request: 

POST /instances
{
  "instance": {
    "name": "products-slave",
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": "fc318e00-3a6f-4f93-af99-146b44912188",
    "flavorRef": "7",
    "volume": {
      "size": 1
    },
    "cluster": {
      "slave": {
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "read_only": true
      }
    }
  }
}

Response: 

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": {
      "id": "fc318e00-3a6f-4f93-af99-146b44912188",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    },
    "cluster": {
      "slave": {
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "read_only": true
      }
    }
  }
}


Show Master


Request: 

GET /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998

Response: 

{
  "instance": {
    "status": "ACTIVE",
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    },
    "cluster": {
      "slaves": [
        {"id": "061aaf4c-3a57-411e-9df9-2d0f813db859"}
      ]
    }
  }
}


Show Slave


Request: 

GET /instances/061aaf4c-3a57-411e-9df9-2d0f813db859

Response: 

{
  "instance": {
    "status": "ACTIVE",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    "name": "products",
    "created": "2014-04-25T20:19:23",
    "updated": "2014-04-25T20:19:23",
    "links": [{...}],
    "datastore": {
      "type": "mysql",
      "version": "5.5"
    },
    "configuration": {
      "id": "fc318e00-3a6f-4f93-af99-146b44912188",
      "links": [{...}],
    },
    "flavor": {
      "id": "7",
      "links": [{...}],
    },
    "volume": {
      "size": 1
    },
    "cluster": {
      "slave": {
        "of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "read_only": true
      }
    }
  }
}


MongoDB


Notes:

  • instance.name will function as the replica-set name
  • The smallest viable deployment pattern for a replica-set is 3 nodes. A three member replica-set can either be (a) a primary and two secondaries or (b) a primary, a secondary, and an arbiter. option (b) provides less redundancy and fault tolerance, so it will not be supported in this first iteration. Therefore, size=3 by default creates a three member replica-set with one primary and two secondaries.
  • instance.cluster.size will only support '3', '5', and '7' as values for MongoDB in this first iteration. Why? (a) an odd number of members ensures the replica-set is always able to elect a primary (b) only 7 members can vote at a time.
    • Scaling the Nodes from 3 to 5, or 5 to 7 will be supported.
    • A replica-set can have up to 12 members, but only 7 voting members. To avoid having to implement and handle 'priority'/'hidden' in the first iteration, the maximum number of nodes is capped at 7.
  • Changing the priority, hidden, slaveDelay, or adding an Arbiter will not be supported in this first iteration.


Couchbase


Notes:

  • instance.cluster.size can be any positive number
  • Scaling the Nodes by increasing the number will be supported.
  • Removing a Node will not be supported in the first iteration.
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