Setting Up Clustering

Clustering Overview

Clustering is a mechanism that enables multiple processes and programs to work together as one entity. For example, when you search for something on google.com, it may seem like your search request is processed by only one web server. In reality, your search request is processed by may web servers connected in a cluster. Similarly, you can have multiple instances of OpenDaylight working together as one entity.

Advantages of clustering are:

  • Scaling: If you have multiple instances of OpenDaylight running, you can potentially do more work and store more data than you could with only one instance. You can also break up your data into smaller chunks (shards) and either distribute that data across the cluster or perform certain operations on certain members of the cluster.
  • High Availability: If you have multiple instances of OpenDaylight running and one of them crashes, you will still have the other instances working and available.
  • Data Persistence: You will not lose any data stored in OpenDaylight after a manual restart or a crash.

The following sections describe how to set up clustering on both individual and multiple OpenDaylight instances.

Multiple Node Clustering

The following sections describe how to set up multiple node clusters in OpenDaylight.

Deployment Considerations

To implement clustering, the deployment considerations are as follows:

  • To set up a cluster with multiple nodes, we recommend that you use a minimum of three machines. You can set up a cluster with just two nodes. However, if one of the two nodes fail, the cluster will not be operational.

    Note

    This is because clustering in OpenDaylight requires a majority of the nodes to be up and one node cannot be a majority of two nodes.

  • Every device that belongs to a cluster needs to have an identifier. OpenDaylight uses the node’s role for this purpose. After you define the first node’s role as member-1 in the akka.conf file, OpenDaylight uses member-1 to identify that node.

  • Data shards are used to contain all or a certain segment of a OpenDaylight’s MD-SAL datastore. For example, one shard can contain all the inventory data while another shard contains all of the topology data.

    If you do not specify a module in the modules.conf file and do not specify a shard in module-shards.conf, then (by default) all the data is placed in the default shard (which must also be defined in module-shards.conf file). Each shard has replicas configured. You can specify the details of where the replicas reside in module-shards.conf file.

  • If you have a three node cluster and would like to be able to tolerate any single node crashing, a replica of every defined data shard must be running on all three cluster nodes.

    Note

    This is because OpenDaylight’s clustering implementation requires a majority of the defined shard replicas to be running in order to function. If you define data shard replicas on two of the cluster nodes and one of those nodes goes down, the corresponding data shards will not function.

  • If you have a three node cluster and have defined replicas for a data shard on each of those nodes, that shard will still function even if only two of the cluster nodes are running. Note that if one of those remaining two nodes goes down, the shard will not be operational.

  • It is recommended that you have multiple seed nodes configured. After a cluster member is started, it sends a message to all of its seed nodes. The cluster member then sends a join command to the first seed node that responds. If none of its seed nodes reply, the cluster member repeats this process until it successfully establishes a connection or it is shut down.

  • After a node is unreachable, it remains down for configurable period of time (10 seconds, by default). Once a node goes down, you need to restart it so that it can rejoin the cluster. Once a restarted node joins a cluster, it will synchronize with the lead node automatically.

Clustering Scripts

OpenDaylight includes some scripts to help with the clustering configuration.

Note

Scripts are stored in the OpenDaylight distribution/bin folder, and maintained in the distribution project repository in the folder distribution-karaf/src/main/assembly/bin/.

Configure Cluster Script

This script is used to configure the cluster parameters (e.g. akka.conf, module-shards.conf) on a member of the controller cluster. The user should restart the node to apply the changes.

Note

The script can be used at any time, even before the controller is started for the first time.

Usage:

bin/configure_cluster.sh <index> <seed_nodes_list>
  • index: Integer within 1..N, where N is the number of seed nodes. This indicates which controller node (1..N) is configured by the script.
  • seed_nodes_list: List of seed nodes (IP address), separated by comma or space.

The IP address at the provided index should belong to the member executing the script. When running this script on multiple seed nodes, keep the seed_node_list the same, and vary the index from 1 through N.

Optionally, shards can be configured in a more granular way by modifying the file “custom_shard_configs.txt” in the same folder as this tool. Please see that file for more details.

Example:

bin/configure_cluster.sh 2 192.168.0.1 192.168.0.2 192.168.0.3

The above command will configure the member 2 (IP address 192.168.0.2) of a cluster made of 192.168.0.1 192.168.0.2 192.168.0.3.

Setting Up a Multiple Node Cluster

To run OpenDaylight in a three node cluster, perform the following:

First, determine the three machines that will make up the cluster. After that, do the following on each machine:

  1. Copy the OpenDaylight distribution zip file to the machine.

  2. Unzip the distribution.

  3. Open the following .conf files:

    • configuration/initial/akka.conf
    • configuration/initial/module-shards.conf
  4. In each configuration file, make the following changes:

    Find every instance of the following lines and replace _127.0.0.1_ with the hostname or IP address of the machine on which this file resides and OpenDaylight will run:

    netty.tcp {
      hostname = "127.0.0.1"
    

    Note

    The value you need to specify will be different for each node in the cluster.

  5. Find the following lines and replace _127.0.0.1_ with the hostname or IP address of any of the machines that will be part of the cluster:

    cluster {
      seed-nodes = ["akka.tcp://opendaylight-cluster-data@${IP_OF_MEMBER1}:2550",
                    <url-to-cluster-member-2>,
                    <url-to-cluster-member-3>]
    
  6. Find the following section and specify the role for each member node. Here we assign the first node with the member-1 role, the second node with the member-2 role, and the third node with the member-3 role:

    roles = [
      "member-1"
    ]
    

    Note

    This step should use a different role on each node.

  7. Open the configuration/initial/module-shards.conf file and update the replicas so that each shard is replicated to all three nodes:

    replicas = [
        "member-1",
        "member-2",
        "member-3"
    ]
    

    For reference, view a sample config files <<_sample_config_files,below>>.

  8. Move into the +<karaf-distribution-directory>/bin+ directory.

  9. Run the following command:

    JAVA_MAX_MEM=4G JAVA_MAX_PERM_MEM=512m ./karaf
    
  10. Enable clustering by running the following command at the Karaf command line:

    feature:install odl-mdsal-clustering
    

OpenDaylight should now be running in a three node cluster. You can use any of the three member nodes to access the data residing in the datastore.

Sample Config Files

Sample akka.conf file:

odl-cluster-data {
  bounded-mailbox {
    mailbox-type = "org.opendaylight.controller.cluster.common.actor.MeteredBoundedMailbox"
    mailbox-capacity = 1000
    mailbox-push-timeout-time = 100ms
  }

  metric-capture-enabled = true

  akka {
    loglevel = "DEBUG"
    loggers = ["akka.event.slf4j.Slf4jLogger"]

    actor {

      provider = "akka.cluster.ClusterActorRefProvider"
      serializers {
                java = "akka.serialization.JavaSerializer"
                proto = "akka.remote.serialization.ProtobufSerializer"
              }

              serialization-bindings {
                  "com.google.protobuf.Message" = proto

              }
    }
    remote {
      log-remote-lifecycle-events = off
      netty.tcp {
        hostname = "10.194.189.96"
        port = 2550
        maximum-frame-size = 419430400
        send-buffer-size = 52428800
        receive-buffer-size = 52428800
      }
    }

    cluster {
      seed-nodes = ["akka.tcp://opendaylight-cluster-data@10.194.189.96:2550",
                    "akka.tcp://opendaylight-cluster-data@10.194.189.98:2550",
                    "akka.tcp://opendaylight-cluster-data@10.194.189.101:2550"]

      auto-down-unreachable-after = 10s

      roles = [
        "member-2"
      ]

    }
  }
}

odl-cluster-rpc {
  bounded-mailbox {
    mailbox-type = "org.opendaylight.controller.cluster.common.actor.MeteredBoundedMailbox"
    mailbox-capacity = 1000
    mailbox-push-timeout-time = 100ms
  }

  metric-capture-enabled = true

  akka {
    loglevel = "INFO"
    loggers = ["akka.event.slf4j.Slf4jLogger"]

    actor {
      provider = "akka.cluster.ClusterActorRefProvider"

    }
    remote {
      log-remote-lifecycle-events = off
      netty.tcp {
        hostname = "10.194.189.96"
        port = 2551
      }
    }

    cluster {
      seed-nodes = ["akka.tcp://opendaylight-cluster-rpc@10.194.189.96:2551"]

      auto-down-unreachable-after = 10s
    }
  }
}

Sample module-shards.conf file:

module-shards = [
    {
        name = "default"
        shards = [
            {
                name="default"
                replicas = [
                    "member-1",
                    "member-2",
                    "member-3"
                ]
            }
        ]
    },
    {
        name = "topology"
        shards = [
            {
                name="topology"
                replicas = [
                    "member-1",
                    "member-2",
                    "member-3"
                ]
            }
        ]
    },
    {
        name = "inventory"
        shards = [
            {
                name="inventory"
                replicas = [
                    "member-1",
                    "member-2",
                    "member-3"
                ]
            }
        ]
    },
    {
         name = "toaster"
         shards = [
             {
                 name="toaster"
                 replicas = [
                    "member-1",
                    "member-2",
                    "member-3"
                 ]
             }
         ]
    }
]

Cluster Monitoring

OpenDaylight exposes shard information via MBeans, which can be explored with JConsole, VisualVM, or other JMX clients, or exposed via a REST API using Jolokia, provided by the odl-jolokia Karaf feature. This is convenient, due to a significant focus on REST in OpenDaylight.

The basic URI that lists a schema of all available MBeans, but not their content itself is:

GET  /jolokia/list

To read the information about the shards local to the queried OpenDaylight instance use the following REST calls. For the config datastore:

GET  /jolokia/read/org.opendaylight.controller:type=DistributedConfigDatastore,Category=ShardManager,name=shard-manager-config

For the operational datastore:

GET  /jolokia/read/org.opendaylight.controller:type=DistributedOperationalDatastore,Category=ShardManager,name=shard-manager-operational

The output contains information on shards present on the node:

{
  "request": {
    "mbean": "org.opendaylight.controller:Category=ShardManager,name=shard-manager-operational,type=DistributedOperationalDatastore",
    "type": "read"
  },
  "value": {
    "LocalShards": [
      "member-1-shard-default-operational",
      "member-1-shard-entity-ownership-operational",
      "member-1-shard-topology-operational",
      "member-1-shard-inventory-operational",
      "member-1-shard-toaster-operational"
    ],
    "SyncStatus": true,
    "MemberName": "member-1"
  },
  "timestamp": 1483738005,
  "status": 200
}

The exact names from the “LocalShards” lists are needed for further exploration, as they will be used as part of the URI to look up detailed info on a particular shard. An example output for the member-1-shard-default-operational looks like this:

{
  "request": {
    "mbean": "org.opendaylight.controller:Category=Shards,name=member-1-shard-default-operational,type=DistributedOperationalDatastore",
    "type": "read"
  },
  "value": {
    "ReadWriteTransactionCount": 0,
    "SnapshotIndex": 4,
    "InMemoryJournalLogSize": 1,
    "ReplicatedToAllIndex": 4,
    "Leader": "member-1-shard-default-operational",
    "LastIndex": 5,
    "RaftState": "Leader",
    "LastCommittedTransactionTime": "2017-01-06 13:19:00.135",
    "LastApplied": 5,
    "LastLeadershipChangeTime": "2017-01-06 13:18:37.605",
    "LastLogIndex": 5,
    "PeerAddresses": "member-3-shard-default-operational: akka.tcp://opendaylight-cluster-data@192.168.16.3:2550/user/shardmanager-operational/member-3-shard-default-operational, member-2-shard-default-operational: akka.tcp://opendaylight-cluster-data@192.168.16.2:2550/user/shardmanager-operational/member-2-shard-default-operational",
    "WriteOnlyTransactionCount": 0,
    "FollowerInitialSyncStatus": false,
    "FollowerInfo": [
      {
        "timeSinceLastActivity": "00:00:00.320",
        "active": true,
        "matchIndex": 5,
        "voting": true,
        "id": "member-3-shard-default-operational",
        "nextIndex": 6
      },
      {
        "timeSinceLastActivity": "00:00:00.320",
        "active": true,
        "matchIndex": 5,
        "voting": true,
        "id": "member-2-shard-default-operational",
        "nextIndex": 6
      }
    ],
    "FailedReadTransactionsCount": 0,
    "StatRetrievalTime": "810.5 μs",
    "Voting": true,
    "CurrentTerm": 1,
    "LastTerm": 1,
    "FailedTransactionsCount": 0,
    "PendingTxCommitQueueSize": 0,
    "VotedFor": "member-1-shard-default-operational",
    "SnapshotCaptureInitiated": false,
    "CommittedTransactionsCount": 6,
    "TxCohortCacheSize": 0,
    "PeerVotingStates": "member-3-shard-default-operational: true, member-2-shard-default-operational: true",
    "LastLogTerm": 1,
    "StatRetrievalError": null,
    "CommitIndex": 5,
    "SnapshotTerm": 1,
    "AbortTransactionsCount": 0,
    "ReadOnlyTransactionCount": 0,
    "ShardName": "member-1-shard-default-operational",
    "LeadershipChangeCount": 1,
    "InMemoryJournalDataSize": 450
  },
  "timestamp": 1483740350,
  "status": 200
}

The output helps identifying shard state (leader/follower, voting/non-voting), peers, follower details if the shard is a leader, and other statistics/counters.

The Integration team is maintaining a Python based tool, that takes advantage of the above MBeans exposed via Jolokia, and the systemmetrics project offers a DLUX based UI to display the same information.

Geo-distributed Active/Backup Setup

An OpenDaylight cluster works best when the latency between the nodes is very small, which practically means they should be in the same datacenter. It is however desirable to have the possibility to fail over to a different datacenter, in case all nodes become unreachable. To achieve that, the cluster can be expanded with nodes in a different datacenter, but in a way that doesn’t affect latency of the primary nodes. To do that, shards in the backup nodes must be in “non-voting” state.

The API to manipulate voting states on shards is defined as RPCs in the cluster-admin.yang file in the controller project, which is well documented. A summary is provided below.

Note

Unless otherwise indicated, the below POST requests are to be sent to any single cluster node.

To create an active/backup setup with a 6 node cluster (3 active and 3 backup nodes in two locations) there is an RPC to set voting states of all shards on a list of nodes to a given state:

POST  /restconf/operations/cluster-admin:change-member-voting-states-for-all-shards

This RPC needs the list of nodes and the desired voting state as input. For creating the backup nodes, this example input can be used:

{
  "input": {
    "member-voting-state": [
      {
        "member-name": "member-4",
        "voting": false
      },
      {
        "member-name": "member-5",
        "voting": false
      },
      {
        "member-name": "member-6",
        "voting": false
      }
    ]
  }
}

When an active/backup deployment already exists, with shards on the backup nodes in non-voting state, all that is needed for a fail-over from the active “sub-cluster” to backup “sub-cluster” is to flip the voting state of each shard (on each node, active AND backup). That can be easily achieved with the following RPC call (no parameters needed):

POST  /restconf/operations/cluster-admin:flip-member-voting-states-for-all-shards

If it’s an unplanned outage where the primary voting nodes are down, the “flip” RPC must be sent to a backup non-voting node. In this case there are no shard leaders to carry out the voting changes. However there is a special case whereby if the node that receives the RPC is non-voting and is to be changed to voting and there’s no leader, it will apply the voting changes locally and attempt to become the leader. If successful, it persists the voting changes and replicates them to the remaining nodes.

When the primary site is fixed and you want to fail back to it, care must be taken when bringing the site back up. Because it was down when the voting states were flipped on the secondary, its persisted database won’t contain those changes. If brought back up in that state, the nodes will think they’re still voting. If the nodes have connectivity to the secondary site, they should follow the leader in the secondary site and sync with it. However if this does not happen then the primary site may elect its own leader thereby partitioning the 2 clusters, which can lead to undesirable results. Therefore it is recommended to either clean the databases (i.e., journal and snapshots directory) on the primary nodes before bringing them back up or restore them from a recent backup of the secondary site (see section Backing Up and Restoring the Datastore).

If is also possible to gracefully remove a node from a cluster, with the following RPC:

POST  /restconf/operations/cluster-admin:remove-all-shard-replicas

and example input:

{
  "input": {
    "member-name": "member-1"
  }
}

or just one particular shard:

POST  /restconf/operations/cluster-admin:remove-shard-replica

with example input:

{
  "input": {
    "shard-name": "default",
    "member-name": "member-2",
    "data-store-type": "config"
  }
}

Now that a (potentially dead/unrecoverable) node was removed, another one can be added at runtime, without changing the configuration files of the healthy nodes (requiring reboot):

POST  /restconf/operations/cluster-admin:add-replicas-for-all-shards

No input required, but this RPC needs to be sent to the new node, to instruct it to replicate all shards from the cluster.

Note

While the cluster admin API allows adding and removing shards dynamically, the module-shard.conf and modules.conf files are still used on startup to define the initial configuration of shards. Modifications from the use of the API are not stored to those static files, but to the journal.