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

m (Summary/Viewpoints/Strategy)
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* Purposefully avoids introducing a /topology (aka /cluster) API
 
* Purposefully avoids introducing a /topology (aka /cluster) API
 
* Purposefully avoids the proliferation of configuration-groups to accomodate mandatory fields in the context of clusters/topologies
 
* Purposefully avoids the proliferation of configuration-groups to accomodate mandatory fields in the context of clusters/topologies
 +
* Purposefully avoids introducing a v2 API
 
* Instead, introduces topology{} field and /instance/<id>/topology routes
 
* Instead, introduces topology{} field and /instance/<id>/topology routes
 
* topology{}'s charter is to include topology/cluster-related fields that are absolutely required to construct the initial cluster/topology.
 
* topology{}'s charter is to include topology/cluster-related fields that are absolutely required to construct the initial cluster/topology.
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* Where possible and logical, consolidate similiar <action>s amongst datastores.
 
* Where possible and logical, consolidate similiar <action>s amongst datastores.
 
<br>
 
<br>
 +
 
== MySQL Master/Slave ==
 
== MySQL Master/Slave ==
 
<br>
 
<br>

Revision as of 05:10, 24 April 2014

Summary/Viewpoints/Strategy


  • Purposefully avoids introducing a /topology (aka /cluster) API
  • Purposefully avoids the proliferation of configuration-groups to accomodate mandatory fields in the context of clusters/topologies
  • Purposefully avoids introducing a v2 API
  • Instead, introduces topology{} field and /instance/<id>/topology routes
  • topology{}'s charter is to include topology/cluster-related fields that are absolutely required to construct the initial cluster/topology.
  • Topology-influenced actions are handled via: 'PUT /instances/<id>/topology', where <id> is any arbitrary node in the topology.
  • Requests against 'PUT /instances/<id>/topology' will follow the format of: { "<action>": { <action_specific_fields> } }
  • Where possible and logical, consolidate similiar <action>s amongst datastores.


MySQL Master/Slave


Create Master


Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    "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": "product-a",
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "name": "config-a",
      "links": [{...}]
    },
    ...
  }
}


Create Slave


Request:

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

Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    "name": "product-b",
    "topology": {
      "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
      "read_only": true
    },
    "configuration": {
      "id": "fc318e00-3a6f-4f93-af99-146b44912188",
      "name": "config-b",
      "links": [{...}]
    },
    ...
  }
}

Notes:

  • For master/slave wirings, the 'server_id' must differ between master and slave, and optionally the slave can specify whether it is read-only or not to avoid accidental writes.
  • Update: Agreed on 03/14/14 that the user should not have to specify 'server_id'. Instead, trove will be responsible for setting it and ensuring that a slave does not have the same server_id as its master, or any sibling slaves. As a part of this agreement, this requires removing 'server_id' from configuration-groups overrides (to avoid the user meddling with our bookkeeping).
  • 'read_only' was removed from configuration-groups and moved to topology{} because forcing the user to create a configuration-group for every MySQL slave is arduous and a poor user experience.
  • 'read_only' is only permitted if 'slave_of' is set, otherwise the request will be failed.
  • Opinion: 'read_only' should default to true if slave_of is set and read_only is not provided.
  • Note: 'slave_of' is purposefully not an array to support multi-source replication coming in 5.7. Instead, a new 'channels' field will be introduced.
  • For now, 'slave_of' requires a vanilla trove instance uuid, but will inevitably need to be prefixed with namespacing to support multiple dcs and sources (e.g. trove:us-west:tenant_id:instance:dfbbd9ca-b5e1-4028-adb7-f78643e17998) and/or additional fields will be added.


Show Instance


Request:

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

Response:

{
  "instance": {
    "status": "ACTIVE",
    "updated": "2014-02-16T03:38:49"
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    "name": "product-a",
    "datastore": {
      "version": "5.5",
      "type": "mysql",
    },
    "flavor": {
      "id": "7",
      "links": [{...}]
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "name": "config-a",
      "links": [{...}]
    }
  }
}


Request:

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

Response:

{
  "instance": {
    "status": "ACTIVE",
    "updated": "2014-02-16T03:38:49"
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    "name": "product-b",
    "datastore": {
      "version": "5.5",
      "type": "mysql",
    },
    "flavor": {
      "id": "7",
      "links": [{...}]
    },
    "topology": {
      "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
      "read_only": true
    },
    "configuration": {
      "id": "b9c8a3f8-7ace-4aea-9908-7b555586d7b6",
      "name": "config-a",
      "links": [{...}]
    }
  }
}


Show Topology


Request:

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

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a"
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "read_only": true
      }
    ]
  }
}


Remove Replication (aka "Promote" to Standalone)


Request:

   POST or PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology/action
or POST or PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "promote": {
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859"
  }
}

Response:

TBD

Notes:

  • The PUT /topology option is more "correct", but POST /action is already an established pattern in the codebase. We must choose one of the four approaches. For the sake of brevity, it is assumed that PUT /topology is chosen (and will be used in examples beyond this point in the document)


MongoDB


Create Replica-Set


Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    ...
    "datastore": {
      "type": "mongodb",
      "version": "2.4.10"
    },
    "topology": {
      "type": "member",
      "cluster_name": "products",
      "join": false
    },
    ...
  }
}

Response:

{
  "instance": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    ...
  }
}


Notes:

  • 'cluster_name' is used as 'replSet'
  • Enforce 'cluster_name' field to be provided for MongoDB, even in the case of a standalone/single instance. See http://www.mongodb.com/blog/post/dont-let-your-standalone-mongodb-server-stand-alone for reasoning.
  • 'join' indicates whether you're joining an existing replica-set, or creating a new one. If 'join' is false, and an active replica-set by that name for the tenant already exists, the request will be failed. 'join' by default will be false, but was included above for illustrative purposes.
  • 'type' is 'member' vs. 'primary' because in a replica-set, the primary is dynamic and can change in an election.


Add Member to Replica-Set


Request:

POST /instances
{
  "instance": {
    "name": "product-b",
    ...
    "topology": {
      "type": "member",
      "cluster_name": "products",
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    ...
  }
}


Notes:

  • If 'join' is true, and there is no existing replica-set for the tenant matching the 'cluster_name' value, the request will be failed.
  • Will have to use 'db.isMaster()' to determine the current primary to execute replica-set commands against (since it can be dynamic due to elections)
  • Will use http://docs.mongodb.org/manual/tutorial/expand-replica-set/#configure-and-add-a-member
  • Should protect against adding more than 12 members to a replica-set
  • Should protect against adding more than 7 voting members to a replica-set
  • Should return warning when number of voting members is even and there is no arbiter


Add Another Member to Replica-Set


Request:

POST /instances
{
  "instance": {
    "name": "product-c",
    ...
    "topology": {
      "type": "member",
      "cluster_name": "products",
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
    ...
  }
}


Show Instance


Request:

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

Response:

{
  "instance": {
    ...
    "topology": {
      "type": "member",
      "cluster_name": "products"
    },
    ...
  }
}


Show Topology


Request:

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

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a",
        "type": "member",
        "cluster_name": "products"
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "type": "member",
        "cluster_name": "products"
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "name": "product-c",
        "type": "member",
        "cluster_name": "products"
      }
    ]
  }
}


Add Arbiter


Request:

POST /instances
{
  "instance": {
    "name": "product-arbiter",
    ...
    "topology": {
      "type": "arbiter",
      "cluster_name": "products",
      "join": true
    },
    ...
  }
}

Response:

{
  "instance": {
    "status": "BUILD",
    "id": "a1b62aaa-7863-4384-8250-59024141c1f8",
    ...
  }
}


Add a Delayed Member


Request:

POST /instances
{
  "instance": {
    "name": "product-delayed",
    ...
    "topology": {
      "type": "member",
      "cluster_name": "products",
      "priority": 0,
      "hidden": true,
      "slaveDelay": 3600,
      "join": true
    },
    ...
  }
}

Response:

{
  "instance": {
    "status": "BUILD",
    "id": "7d8eb019-931b-4b2a-88d2-4c9f0ca1b29e",
    ...
  }
}


Notes:

  • 'type', 'cluster_name', 'join', 'priority', 'hidden', and 'slaveDelay' are the only fields supported in topology{} for mongodb. All other configuration values must be set via a configuration-group. After more thought, consider supporting 'hostname' and 'votes' as well.
  • Why isn't 'priority', 'hidden' and 'slaveDelay' in a configuration-group you ask? This is explained in "Modifying a Replica-Set" below.


Modifying a Replica-Set


Thus far we've been able to model building a replica-set, adding an arbiter, adding a delayed secondary member, etc. Let's continue with how to modify a replica-set.

Example:

# from http://docs.mongodb.org/manual/tutorial/configure-secondary-only-replica-set-member/#example
cfg = rs.conf()
cfg.members[0].priority = 2
cfg.members[1].priority = 1
cfg.members[2].priority = 0.5
cfg.members[3].priority = 0
rs.reconfig(cfg)

Executing these priority changes one at a time can have catastrophic results, so it must be done as a transaction (with rs.reconfig() commiting). However, without the ability to address the cluster (i.e. multiple members at once), this becomes impossible. The only backdoor solution would be to guarantee that the MongoDB user(s) presented to the cloud tenant all have the clusterAdmin role, as this would allow them to connect to the primary and execute such transactions themselves via the native client. Obviously however, granting clusterAdmin to every DBaaS user in MongoDB is unacceptable in most deployments. The solution is as follows:

Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology
{
  "update_member_attributes": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "priority": 2
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "priority": 1
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "priority": 0.5
      }
    ]
  }
}


Notes:



Remove a Member


Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "promote": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
  }
}


Notes:



MongoDB TokuMX

  • TokuMUX will require a new datastore-version and *possibly* a new manager class (same reasoning as why Tungsten/Galera will have their own datastore-version for MySQL)



Cassandra


Create Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    ...
    "datastore": {
      "type": "cassandra",
      "version": "cassandra-2.0.5"
    },
    "topology": {
      "cluster_name": "products",
      "num_tokens": 256,
      "is_seed": true,
      "endpoint_snitch": "RackInferringSnitch",
      "join": false
    },
    ...
  }
}

Response:

{
  "instance": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    ...
  }
}


Notes:

  • Unlike in MongoDB, the 'type' field is not required (because all members of the cluster are of the same type)
  • 'cluster_name', 'num_tokens', and 'is_seed' are always required, with 'endpoint_snitch' being required if 'join' is false (if 'join' is true, the endpoint_snitch is inherited) and 'auto_bootstrap' required if 'join' is true.
  • 'seed_provider' can optionally be provided, but conveniently defaults to 'org.apache.cassandra.locator.SimpleSeedProvider'
  • 'join' indicates whether you're joining an existing cluster, or creating a new one. If 'join' is false, and an active cluster by that name for the tenant already exists, the request will be failed. 'join' by default will be false, but was included above for illustrative purposes.
  • Likely the Keystone region and the availability-zone inherent to the trove request can be used for the data-center and rack (cassandra-topology.properties), but if it turns out that the naming schemes are incompatible, 'data_center' and 'rack' can be introduced.
  • 'is_seed' is used vs. a seed list of ip-addresses because (1) the ip-address is not yet known and (2) when additional seeds are added, each node in the cluster must be notified and updated. More on this later.


Add Node to Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-b",
    ...
    "topology": {
      "cluster_name": "products",
      "num_tokens": 256,
      "is_seed": false,
      "auto_bootstrap": false,
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    ...
  }
}


Notes:

  • If 'join' is true, and there is no existing cluster for the tenant matching the 'cluster_name' value, the request will be failed.
  • If 'endpoint_snitch' is provided, and the value does not match that of the existing node(s) in the cluster, the request will be failed.


Add Another Node to Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-c",
    ...
    "topology": {
      "cluster_name": "products",
      "num_tokens": 256,
      "is_seed": false,
      "auto_bootstrap": false,
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
    ...
  }
}


Show Instance


Request:

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

Response:

{
  "instance": {
    ...
    "topology": {
      "cluster_name": "products",
      "num_tokens": 256,
      "is_seed": true
    },
    ...
  }
}


Show Topology


Request:

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

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a",
        "cluster_name": "products",
        "num_tokens": 256,
        "is_seed": true
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "cluster_name": "products",
        "num_tokens": 256,
        "is_seed": false
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "name": "product-c",
        "cluster_name": "products",
        "num_tokens": 256,
        "is_seed": false
      }
    ]
  }
}


Modifying a Cluster


Example: Drain (http://www.datastax.com/documentation/cassandra/2.0/cassandra/tools/toolsDrain.html)

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology
{
  "drain_node": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
  }
}


Remove a Member


Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology
{
  "promote": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
  }
}


Notes:


Couchbase


Create Cluster


Create Initial Cluster

Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    ...
    "datastore": {
      "type": "couchbase",
      "version": "2.5.1"
    },
    "topology": {
      "cluster_name": "products",
      "join": false
    },
    ...
  }
}

Response:

{
  "instance": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    ...
  }
}


Notes:


Add Node to Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-b",
    ...
    "topology": {
      "cluster_name": "products",
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    ...
  }
}


Notes:

  • If 'join' is true, and there is no existing cluster for the tenant matching the 'cluster_name' value, the request will be failed.
  • In Couchbase, a new node can join the cluster by referencing any existing member, which is discoverable by trove via the cluster_name (unique per tenant)


Add Another Node to Cluster


Request/Response omitted due to a lack of any special considerations required

Show Instance


Request/Response omitted due to a lack of any special considerations required

Show Topology


Request/Response omitted due to a lack of any special considerations required

Modifying a Cluster


Example: Create Bucket

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "create_bucket": {
    "bucket": "test_bucket",
    "bucket_type": "couchbase",
    "bucket_port": 11222,
    "bucket_ramsize": 200,
    "bucket_replica": 1
  }
}


Remove a Member


Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "failover": {
    "ids": ["dfbbd9ca-b5e1-4028-adb7-f78643e17998"],
    "rebalance": true
  }
}


Notes:

  • As noted in the Couchbase documentation, removing a node is akin to a failover and has extreme impliciations. For this reason, "promote" was not used (that, and "rebalance" is optional.)



Redis


Create Master


Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    ...
    "datastore": {
      "type": "redis",
      "version": "2.8.6"
    },
    ...
  }
}

Response:

{
  "instance": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    ...
  }
}


Notes:

  • topology{} is not required for redis
  • note: 'join' field is not required for redis. also notice the lack of a 'cluster_name' of sorts (see 'Add Slave' for reasoning)


Add Slave


Request:

POST /instances
{
  "instance": {
    "name": "product-b",
    ...
    "datastore": {
      "type": "redis",
      "version": "2.8.6"
    },
    "topology": {
      "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    ...
  }
}


Notes:

  • redis supports daisy-chaining slaves, therefore the 'slave_of' value needs to be a specific trove instance uuid vs. a manufactured 'cluster_name' of sorts.
  • whether it is a master or slave can be inferred from the presence (or lack thereof) of 'slave_of'.
  • note that 'slave_of' is also used for mysql (the datastore information will have to be used to determine the semantic difference)


Show Instance


Request:

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

Response:

{
  "instance": {
    ...
  }
}


Show Topology


Request:

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

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a"
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
      }
    ]
  }
}


Promote/Disconnect Slave


Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "promote": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
  }
}


Notes:

  • note that 'promote' is also used for mysql (the datastore information will have to be used to determine the semantic difference)


Redis Cluster


Create Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-a",
    ...
    "datastore": {
      "type": "redis",
      "version": "3.0.0-beta1"
    },
    "topology": {
      "cluster_name": "products",
      "join": false
    },
    ...
  }
}

Response:

{
  "instance": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    ...
  }
}


Notes:

  • Will require datastore-version (to 'manager' to topology{}) validation that cluster_name is supported for redis (because redis 3.x supports clusters, whereas 2.x does not)
  • 'cluster-node-timeout' should be handled by configuration by the deployer (outside the context of configuration-group).
  • Note: shares 'cluster_name' with Cassandra.


Add Another Master to Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-b",
    ...
    "datastore": {
      "type": "redis",
      "version": "3.0.0-beta1"
    },
    "topology": {
      "cluster_name": "products",
      "join": true
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    ...
  }
}


Add Slave to Cluster


Request:

POST /instances
{
  "instance": {
    "name": "product-c",
    ...
    "datastore": {
      "type": "redis",
      "version": "3.0.0-beta1"
    },
    "topology": {
      "cluster_name": "products",
      "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
    },
    ...
  }
}


Response:

{
  "instance": {
    "status": "BUILD",
    "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
    ...
  }
}


Notes:

  • Despite redis clusters supporting the ability to add a slave without designating the master, we will require it to avoid unoptimal geographical relationships.


Show Instance


Request:

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

Response:

{
  "instance": {
    ...
    "topology": {
      "cluster_name": "products"
    },
    ...
  }
}


Show Topology


Request:

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

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a",
        "cluster_name": "products"
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "cluster_name": "products"
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "name": "product-c",
        "cluster_name": "products"
        "slave_of": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
      }
    ]
  }
}


Promote/Disconnect Slave


Work in Progress

Summary


Summary of topology{} Fields

Field Datastore(s)
slave_of mysql, redis, redis-cluster
read_only mysql
type mongodb
cluster_name mongodb, cassandra, couchbase, redis-cluster
priority mongodb
hidden mongodb
slaveDelay mongodb
hostname mongodb
votes mongodb
num_tokens cassandra
is_seed cassandra
endpoint_snitch cassandra
auto_bootstrap cassandra
join mongodb, cassandra, couchbase, redis-cluster


Questions:

  • Is this an acceptable number of added fields, is it confusing, and is the growth of fields as we add more datastores sustainable?


Summary of Route Changes


New Routes:

GET /instances/<id>/topology
{
  "topology": {
    "members": [
      {
        "id": "<id>",
        "name": "<name>",
        <datastore-specific topology fields>
      },
      <repeat>
    ]
  }
}
PUT /instances/<id>/topology
{
  "<action>": {
    <action-specific fields, with one or more including the targeted id(s)>
  }
}


Open Questions


  • How to handle launching multiple nodes with one request? Adding a num_nodes field is a bit of a mismatch (considering the route remains /instance) it and assumes all nodes are homogenous w/ respect to flavor, configuration-group, etc. Or is the user changing these things after the cluster is up acceptable?


Discussion Points


Replica-Set Member Type/Attribute Updates



Option #1: PATCH /instances/:id/topology

Request:

PATCH /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "members": [
    {
      "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
      "priority": 2
    },
    {
      "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
      "priority": 1
    },
    {
      "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
      "priority": 0.5
    }
  ]
}

Response:

{
  "topology": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "name": "product-a",
        "type": "member",
        "cluster_name": "products"
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "name": "product-b",
        "type": "member",
        "cluster_name": "products"
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "name": "product-c",
        "type": "member",
        "cluster_name": "products"
      }
    ]
  }
}


Notes:

  • An HTTP PATCH vs. PUT because the omission of a field should not be an indication to drop/delete it.
  • All modified fields in a request will be changed transactionally in a single rs.reconfig().
  • It should now be clear why 'priority', 'hidden' and 'slaveDelay' are in topology{} vs. a configuration-group: when a configuration-group is changed, an event is immediately triggered to update any attached trove instances. Therefore, if you have a heterogeneous mixture of configuration-groups in a replica-set, there is no way to coordinate a consolidated rs.reconfig().
  • Downside: topology{} may have fields returned on a GET that you cannot change in a PATCH/PUT; re-worded, the granularity of what is permissible to change in a PATCH becomes complicated to check and validate.
  • TBD on what should be returned in the topology{} on a GET /instance/:id and GET /instance/:id/topology. It's a question of whether we should persist anything beyond the 'type' and 'cluster_name'. If say the 'priority' is stored, you introduce the possibility of drift from the truth, but can easily return it on a GET; if it's not stored, do we prompt MongoDB for the truth on a GET, or is that too computationally expensive?



Option #2: POST /instances/:id/topology/action

Request:

   POST or PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology/action
or POST or PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "update_member_attributes": {
    "members": [
      {
        "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
        "priority": 2
      },
      {
        "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
        "priority": 1
      },
      {
        "id": "3a72ee87-cf3e-40f1-a1e1-fe8c7263a782",
        "priority": 0.5
      }
    ]
  }
}


Notes:

  • 'update_member_attributes.members[]' elements will only permit 'priority', 'hidden', and 'slaveDelay' (possibly 'votes' and 'hostname' as mentioned earlier).
  • Due to the limited field-set, this approach is much more fine-grained than the PATCH approach in Option #1.



Decision: Option #2 is more fine-grained, easier to reason about, and less error-prone. As you'll see in later operations (like Remove a Member), is also more appropriate.

Remove a Member from a Replica-Set


Removing a member from a topology/cluster is not the same as deleting one, therefore DELETE /instances/:id is not appropriate.

Option #1: PUT /instances/:id/topology

Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "members": [
    {
      "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998",
    },
    {
      "id": "061aaf4c-3a57-411e-9df9-2d0f813db859",
    }
  ]
}


Notes:

  • By omitting a member{} for id=3a72ee87-cf3e-40f1-a1e1-fe8c7263a782 in a PUT operation, this indicates the member should be removed from the replica-set.
  • It's possible that one might want to modify the 'priority', 'hidden', 'votes', etc. fields of the remaining members while dropping a member. So although the example above does not show it, mongodb{} can be included in a member to indicate other changes, *BUT*, since it's a PUT the expectation of what happens to omitted fields in mongodb{} becomes unclear.


Summary: Not very clean, mildly confusing, and very error-prone (nowhere is a "remove" action ever explicitly implied).

Option #2: POST /instances/:id/topology/action

Request:

PUT /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology

{
  "remove_member": {
    "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
  }
}


Notes:

  • The 'remove_member' action is explicit here, vs. implicit as seen in the prior example.
  • 'remove_member' has a strict set of fields that are supported, so there is no question as to what can be provided and what will be honored (as compared to Option #1).
  • Note: Could rename remove_member here to 'promote'!


Summary: Fairly clean, with no real drawbacks.

Option #3: POST /instances/:id/topology/remove

POST /instances/dfbbd9ca-b5e1-4028-adb7-f78643e17998/topology/remove

{
  "id": "dfbbd9ca-b5e1-4028-adb7-f78643e17998"
}


Notes:

  • Differs from Option #2 in that the action is in the URI vs. the payload (which is considered incorrect in REST due to it being a verb)
  • One drawback of this approach is that not every action will be supported across all datastores. So for example, a POST /instances/:id/topology/changeoplogsize (http://docs.mongodb.org/manual/tutorial/change-oplog-size/) makes absolutely no sense to any datastore other than MongoDB.


Summary: At first glance it might look cleaner than Option #2 from a payload-perspective, but the URI discoverability and expansion is awful.

Option #4: POST /instances/:id/action

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

{
  "join": false
}


Notes:

  • Executed against the instance you wish to remove itself from the cluster, so providing the 'id' in the payload is unnecessary.
  • Drawback: There are actions that are replica-set-wide (or against a subset of the replica-set), meaning Option #1 or #2 or #3 would have to co-exist with this option anyway.
  • Drawback: Increase the number of ways to accomplish the same thing (could unjoin against /instances/:id/action, or against /instances/:id/topology)


Summary: For this very specific example it looks great, but isn't expressive enough for other actions.

Option #5: POST /instances/:id/topology/:id/action

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

{
  "remove": {}
}


Notes:

  • The /instances/:id is an arbitrary member in the replica-set, it doesn't matter which one; the topology/:id is then a member of said replica-set that this action will be applied to.
  • Executed against the instance you wish to remove itself from the cluster, so providing the 'id' in the payload is unnecessary.
  • Needs More Thought: Could conceivably allow only specific operations here (like remove/unjoin), but not others that could be accomplished in a PATCH against /instances/:id/topology (like 'priority', 'hidden', etc.)


Summary: Fairly clean with no real drawbacks.