$ sudo service kudu-master start
$ sudo service kudu-tserver start| Kudu is easier to manage with Cloudera Manager than in a standalone installation. See Cloudera’s Kudu documentation for more details about using Kudu with Cloudera Manager. |
These instructions are relevant only when Kudu is installed using operating system packages
(e.g. rpm or deb).
|
Start Kudu services using the following commands:
$ sudo service kudu-master start
$ sudo service kudu-tserver startTo stop Kudu services, use the following commands:
$ sudo service kudu-master stop
$ sudo service kudu-tserver stopKudu tablet servers and masters expose useful operational information on a built-in web interface,
Kudu master processes serve their web interface on port 8051. The interface exposes several pages with information about the cluster state:
A list of tablet servers, their host names, and the time of their last heartbeat.
A list of tables, including schema and tablet location information for each.
SQL code which you can paste into Impala Shell to add an existing table to Impala’s list of known data sources.
Each tablet server serves a web interface on port 8050. The interface exposes information about each tablet hosted on the server, its current state, and debugging information about maintenance background operations.
Both Kudu masters and tablet servers expose a common set of information via their web interfaces:
HTTP access to server logs.
an /rpcz endpoint which lists currently running RPCs via JSON.
pages giving an overview and detailed information on the memory usage of different components of the process.
information on the current set of configuration flags.
information on the currently running threads and their resource consumption.
a JSON endpoint exposing metrics about the server.
information on the deployed version number of the daemon.
These interfaces are linked from the landing page of each daemon’s web UI.
Kudu daemons expose a large number of metrics. Some metrics are associated with an entire server process, whereas others are associated with a particular tablet replica.
The full set of available metrics for a Kudu server can be dumped via a special command line flag:
$ kudu-tserver --dump_metrics_json
$ kudu-master --dump_metrics_jsonThis will output a large JSON document. Each metric indicates its name, label, description, units, and type. Because the output is JSON-formatted, this information can easily be parsed and fed into other tooling which collects metrics from Kudu servers.
Metrics can be collected from a server process via its HTTP interface by visiting
/metrics. The output of this page is JSON for easy parsing by monitoring services.
This endpoint accepts several GET parameters in its query string:
/metrics?metrics=<substring1>,<substring2>,… - limits the returned metrics to those which contain
at least one of the provided substrings. The substrings also match entity names, so this
may be used to collect metrics for a specific tablet.
/metrics?include_schema=1 - includes metrics schema information such as unit, description,
and label in the JSON output. This information is typically elided to save space.
/metrics?compact=1 - eliminates unnecessary whitespace from the resulting JSON, which can decrease
bandwidth when fetching this page from a remote host.
/metrics?include_raw_histograms=1 - include the raw buckets and values for histogram metrics,
enabling accurate aggregation of percentile metrics over time and across hosts.
For example:
$ curl -s 'http://example-ts:8050/metrics?include_schema=1&metrics=connections_accepted'[
{
"type": "server",
"id": "kudu.tabletserver",
"attributes": {},
"metrics": [
{
"name": "rpc_connections_accepted",
"label": "RPC Connections Accepted",
"type": "counter",
"unit": "connections",
"description": "Number of incoming TCP connections made to the RPC server",
"value": 92
}
]
}
]$ curl -s 'http://example-ts:8050/metrics?metrics=log_append_latency'[
{
"type": "tablet",
"id": "c0ebf9fef1b847e2a83c7bd35c2056b1",
"attributes": {
"table_name": "lineitem",
"partition": "hash buckets: (55), range: [(<start>), (<end>))",
"table_id": ""
},
"metrics": [
{
"name": "log_append_latency",
"total_count": 7498,
"min": 4,
"mean": 69.3649,
"percentile_75": 29,
"percentile_95": 38,
"percentile_99": 45,
"percentile_99_9": 95,
"percentile_99_99": 167,
"max": 367244,
"total_sum": 520098
}
]
}
]| All histograms and counters are measured since the server start time, and are not reset upon collection. |
Kudu may be configured to periodically dump all of its metrics to a local log file using the
--metrics_log_interval_ms flag. Set this flag to the interval at which metrics should be written
to a log file.
The metrics log will be written to the same directory as the other Kudu log files, with the same naming format. After any metrics log file reaches 64MB uncompressed, the log will be rolled and the previous file will be gzip-compressed.
The log file generated has three space-separated fields. The first field is the word
metrics. The second field is the current timestamp in microseconds since the Unix epoch.
The third is the current value of all metrics on the server, using a compact JSON encoding.
The encoding is the same as the metrics fetched via HTTP described above.
| Although metrics logging automatically rolls and compresses previous log files, it does not remove old ones. Since metrics logging can use significant amounts of disk space, consider setting up a system utility to monitor space in the log directory and archive or delete old segments. |
For high availability and to avoid a single point of failure, Kudu clusters should be created with multiple masters. Many Kudu clusters were created with just a single master, either for simplicity or because Kudu multi-master support was still experimental at the time. This workflow demonstrates how to migrate to a multi-master configuration.
| The workflow is unsafe for adding new masters to an existing multi-master configuration. Do not use it for that purpose. |
| The workflow presupposes at least basic familiarity with Kudu configuration management. If using Cloudera Manager (CM), the workflow also presupposes familiarity with it. |
All of the command line steps below should be executed as the Kudu UNIX user, typically
kudu.
|
Establish a maintenance window (one hour should be sufficient). During this time the Kudu cluster will be unavailable.
Decide how many masters to use. The number of masters should be odd. Three or five node master configurations are recommended; they can tolerate one or two failures respectively.
Perform the following preparatory steps for the existing master:
Identify and record the directory where the master’s data lives. If using Kudu system packages,
the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and
fs_data_dirs configuration parameter. Please note if you’ve set fs_data_dirs to some directories
other than the value of fs_wal_dir, it should be explicitly included in every command below where
fs_wal_dir is also included.
Identify and record the port the master is using for RPCs. The default port value is 7051, but it
may have been customized using the rpc_bind_addresses configuration parameter.
Identify the master’s UUID. It can be fetched using the following command:
$ kudu fs dump uuid --fs_wal_dir=<master_data_dir> 2>/dev/nullexisting master’s previously recorded data directory
$ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null 4aab798a69e94fab8d77069edff28ce0
Optional: configure a DNS alias for the master. The alias could be a DNS cname (if the machine
already has an A record in DNS), an A record (if the machine is only known by its IP address),
or an alias in /etc/hosts. The alias should be an abstract representation of the master (e.g.
master-1).
| Without DNS aliases it is not possible to recover from permanent master failures, and as such it is highly recommended. |
Perform the following preparatory steps for each new master:
Choose an unused machine in the cluster. The master generates very little load so it can be colocated with other data services or load-generating processes, though not with another Kudu master from the same configuration.
Ensure Kudu is installed on the machine, either via system packages (in which case the kudu and
kudu-master packages should be installed), or via some other means.
Choose and record the directory where the master’s data will live.
Choose and record the port the master should use for RPCs.
Optional: configure a DNS alias for the master (e.g. master-2, master-3, etc).
Stop all the Kudu processes in the entire cluster.
Format the data directory on each new master machine, and record the generated UUID. Use the following command sequence:
$ kudu fs format --fs_wal_dir=<master_data_dir>
$ kudu fs dump uuid --fs_wal_dir=<master_data_dir> 2>/dev/nullnew master’s previously recorded data directory
$ kudu fs format --fs_wal_dir=/var/lib/kudu/master $ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null f5624e05f40649b79a757629a69d061e
If using CM, add the new Kudu master roles now, but do not start them.
If using DNS aliases, override the empty value of the Master Address parameter for each role
(including the existing master role) with that master’s alias.
Add the port number (separated by a colon) if using a non-default RPC port value.
Rewrite the master’s Raft configuration with the following command, executed on the existing master machine:
$ kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=<master_data_dir> <tablet_id> <all_masters>existing master’s previously recorded data directory
must be the string 00000000000000000000000000000000
space-separated list of masters, both new and existing. Each entry in the list must be
a string of the form <uuid>:<hostname>:<port>
master’s previously recorded UUID
master’s previously recorded hostname or alias
master’s previously recorded RPC port number
$ kudu local_replica cmeta rewrite_raft_config --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 4aab798a69e94fab8d77069edff28ce0:master-1:7051 f5624e05f40649b79a757629a69d061e:master-2:7051 988d8ac6530f426cbe180be5ba52033d:master-3:7051
Modify the value of the master_addresses configuration parameter for both existing master and new masters.
The new value must be a comma-separated list of all of the masters. Each entry is a string of the form <hostname>:<port>
master’s previously recorded hostname or alias
master’s previously recorded RPC port number
Start the existing master.
Copy the master data to each new master with the following command, executed on each new master machine:
$ kudu local_replica copy_from_remote --fs_wal_dir=<master_data_dir> <tablet_id> <existing_master>new master’s previously recorded data directory
must be the string 00000000000000000000000000000000
RPC address of the existing master and must be a string of the form
<hostname>:<port>
existing master’s previously recorded hostname or alias
existing master’s previously recorded RPC port number
$ kudu local_replica copy_from_remote --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 master-1:7051
Start all of the new masters.
| Skip the next step if using CM. |
Modify the value of the tserver_master_addrs configuration parameter for each tablet server.
The new value must be a comma-separated list of masters where each entry is a string of the form
<hostname>:<port>
master’s previously recorded hostname or alias
master’s previously recorded RPC port number
Start all of the tablet servers.
Congratulations, the cluster has now been migrated to multiple masters! To verify that all masters are working properly, consider performing the following sanity checks:
Using a browser, visit each master’s web UI. Look at the /masters page. All of the masters should be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.
Run a Kudu system check (ksck) on the cluster using the kudu command line
tool. See Checking Cluster Health with ksck for more details.
Kudu multi-master deployments function normally in the event of a master loss. However, it is important to replace the dead master; otherwise a second failure may lead to a loss of availability, depending on the number of available masters. This workflow describes how to replace the dead master.
Due to KUDU-1620, it is not possible to perform this workflow without also restarting the live masters. As such, the workflow requires a maintenance window, albeit a brief one as masters generally restart quickly.
| Kudu does not yet support Raft configuration changes for masters. As such, it is only possible to replace a master if the deployment was created with DNS aliases. See the multi-master migration workflow for more details. |
| The workflow presupposes at least basic familiarity with Kudu configuration management. If using Cloudera Manager (CM), the workflow also presupposes familiarity with it. |
All of the command line steps below should be executed as the Kudu UNIX user, typically
kudu.
|
Ensure that the dead master is well and truly dead. Take whatever steps needed to prevent it from accidentally restarting; this can be quite dangerous for the cluster post-recovery.
Choose one of the remaining live masters to serve as a basis for recovery. The rest of this workflow will refer to this master as the "reference" master.
Choose an unused machine in the cluster where the new master will live. The master generates very little load so it can be colocated with other data services or load-generating processes, though not with another Kudu master from the same configuration. The rest of this workflow will refer to this master as the "replacement" master.
Perform the following preparatory steps for the replacement master:
Ensure Kudu is installed on the machine, either via system packages (in which case the kudu and
kudu-master packages should be installed), or via some other means.
Choose and record the directory where the master’s data will live.
Perform the following preparatory steps for each live master:
Identify and record the directory where the master’s data lives. If using Kudu system packages,
the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and
fs_data_dirs configuration parameter. Please note if you’ve set fs_data_dirs to some directories
other than the value of fs_wal_dir, it should be explicitly included in every command below where
fs_wal_dir is also included.
Identify and record the master’s UUID. It can be fetched using the following command:
$ kudu fs dump uuid --fs_wal_dir=<master_data_dir> 2>/dev/nulllive master’s previously recorded data directory
$ kudu fs dump uuid --fs_wal_dir=/var/lib/kudu/master 2>/dev/null 80a82c4b8a9f4c819bab744927ad765c
Perform the following preparatory steps for the reference master:
Identify and record the directory where the master’s data lives. If using Kudu system packages,
the default value is /var/lib/kudu/master, but it may be customized via the fs_wal_dir and
fs_data_dirs configuration parameter. Please note if you’ve set fs_data_dirs to some directories
other than the value of fs_wal_dir, it should be explicitly included in every command below where
fs_wal_dir is also included.
Identify and record the UUIDs of every master in the cluster, using the following command:
$ kudu local_replica cmeta print_replica_uuids --fs_wal_dir=<master_data_dir> <tablet_id> 2>/dev/nullreference master’s previously recorded data directory
must be the string 00000000000000000000000000000000
$ kudu local_replica cmeta print_replica_uuids --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 2>/dev/null 80a82c4b8a9f4c819bab744927ad765c 2a73eeee5d47413981d9a1c637cce170 1c3f3094256347528d02ec107466aef3
Using the two previously-recorded lists of UUIDs (one for all live masters and one for all masters), determine and record (by process of elimination) the UUID of the dead master.
Format the data directory on the replacement master machine using the previously recorded UUID of the dead master. Use the following command sequence:
$ kudu fs format --fs_wal_dir=<master_data_dir> --uuid=<uuid>replacement master’s previously recorded data directory
dead master’s previously recorded UUID
$ kudu fs format --fs_wal_dir=/var/lib/kudu/master --uuid=80a82c4b8a9f4c819bab744927ad765c
Copy the master data to the replacement master with the following command:
$ kudu local_replica copy_from_remote --fs_wal_dir=<master_data_dir> <tablet_id> <reference_master>replacement master’s previously recorded data directory
must be the string 00000000000000000000000000000000
RPC address of the reference master and must be a string of the form
<hostname>:<port>
reference master’s previously recorded hostname or alias
reference master’s previously recorded RPC port number
$ kudu local_replica copy_from_remote --fs_wal_dir=/var/lib/kudu/master 00000000000000000000000000000000 master-2:7051
If using CM, add the replacement Kudu master role now, but do not start it.
Override the empty value of the Master Address parameter for the new role with the replacement
master’s alias.
Add the port number (separated by a colon) if using a non-default RPC port value.
Reconfigure the DNS alias for the dead master to point at the replacement master.
Start the replacement master.
Restart the existing live masters. This results in a brief availability outage, but it should last only as long as it takes for the masters to come back up.
Congratulations, the dead master has been replaced! To verify that all masters are working properly, consider performing the following sanity checks:
Using a browser, visit each master’s web UI. Look at the /masters page. All of the masters should be listed there with one master in the LEADER role and the others in the FOLLOWER role. The contents of /masters on each master should be the same.
Run a Kudu system check (ksck) on the cluster using the kudu command line
tool. See Checking Cluster Health with ksck for more details.
ksckThe kudu CLI includes a tool named ksck which can be used for checking
cluster health and data integrity. ksck will identify issues such as
under-replicated tablets, unreachable tablet servers, or tablets without a
leader.
ksck should be run from the command line, and requires the full list of master
addresses to be specified:
$ kudu cluster ksck master-01.example.com,master-02.example.com,master-03.example.comTo see a full list of the options available with ksck, use the --help flag.
If the cluster is healthy, ksck will print a success message, and return a
zero (success) exit status.
Connected to the Master Fetched info from all 1 Tablet Servers Table IntegrationTestBigLinkedList is HEALTHY (1 tablet(s) checked) The metadata for 1 table(s) is HEALTHY OK
If the cluster is unhealthy, for instance if a tablet server process has
stopped, ksck will report the issue(s) and return a non-zero exit status:
Connected to the Master WARNING: Unable to connect to Tablet Server 8a0b66a756014def82760a09946d1fce (tserver-01.example.com:7050): Network error: could not send Ping RPC to server: Client connection negotiation failed: client connection to 192.168.0.2:7050: connect: Connection refused (error 61) WARNING: Fetched info from 0 Tablet Servers, 1 weren't reachable Tablet ce3c2d27010d4253949a989b9d9bf43c of table 'IntegrationTestBigLinkedList' is unavailable: 1 replica(s) not RUNNING 8a0b66a756014def82760a09946d1fce (tserver-01.example.com:7050): TS unavailable [LEADER] Table IntegrationTestBigLinkedList has 1 unavailable tablet(s) WARNING: 1 out of 1 table(s) are not in a healthy state ================== Errors: ================== error fetching info from tablet servers: Network error: Not all Tablet Servers are reachable table consistency check error: Corruption: 1 table(s) are bad FAILED Runtime error: ksck discovered errors
To verify data integrity, the optional --checksum_scan flag can be set, which
will ensure the cluster has consistent data by scanning each tablet replica and
comparing results. The --tables or --tablets flags can be used to limit the
scope of the checksum scan to specific tables or tablets, respectively. For
example, checking data integrity on the IntegrationTestBigLinkedList table can
be done with the following command:
$ kudu cluster ksck --checksum_scan --tables IntegrationTestBigLinkedList master-01.example.com,master-02.example.com,master-03.example.comKudu tablet servers are not resilient to disk failure. When a disk containing a data directory or the write-ahead log (WAL) dies, the entire tablet server must be rebuilt. Kudu will automatically re-replicate tablets on other servers after a tablet server fails, but manual intervention is needed in order to restore the failed tablet server to a running state.
The first step to restoring a tablet server after a disk failure is to replace
the failed disk, or remove the failed disk from the data-directory and/or WAL
configuration. Next, the contents of the data directories and WAL directory must
be removed. For example, if the tablet server is configured with
--fs_wal_dir=/data/0/kudu-tserver-wal and
--fs_data_dirs=/data/1/kudu-tserver,/data/2/kudu-tserver, the following
commands will remove the data directories and WAL directory contents:
$ rm -rf /data/0/kudu-tserver-wal/* /data/1/kudu-tserver/* /data/2/kudu-tserver/*After the WAL and data directories are emptied, the tablet server process can be
started. When Kudu is installed using system packages, service is typically
used:
$ sudo service kudu-tserver startOnce the tablet server is running again, new tablet replicas will be created on it as necessary.