This page shows you how to decommission one or more nodes. Decommissioning a node removes it from the CockroachDB cluster.

You might do this, for example, when downsizing a cluster or reacting to hardware failures.

Note:

Node decommissioning should not be performed when upgrading your cluster's version of CockroachDB or performing planned maintenance (e.g., upgrading system software). In these scenarios, you will want to temporarily stop the node and restart it later.

Overview

How it works

A node is considered to be decommissioned when it meets two criteria:

  1. The node has completed the decommissioning process.
  2. The node has been stopped and has not updated its liveness record for the duration configured via server.time_until_store_dead, which defaults to 5 minutes.

The decommissioning process transfers all range replicas on the node to other nodes. During and after this process, the node is considered "decommissioning" and continues to accept new SQL connections. Even without replicas, the node can still function as a gateway to route connections to relevant data. For this reason, the /health?ready=1 monitoring endpoint continues to consider the node "ready" so load balancers can continue directing traffic to the node.

After all range replicas have been transferred, it's typical to drain the node of SQL clients and distributed SQL queries. The node can then be stopped via a process manager or orchestration tool, or by sending SIGTERM manually. When stopped, the /health?ready=1 monitoring endpoint starts returning a 503 Service Unavailable status response code so that load balancers stop directing traffic to the node. At this point the node stops updating its liveness record, and after the duration configured via server.time_until_store_dead is considered to be decommissioned.

You can check the status of node decommissioning with the CLI.

Considerations

Before decommissioning a node, make sure other nodes are available to take over the range replicas from the node. If no other nodes are available, the decommissioning process will hang indefinitely. See the Examples below for more details.

Examples

3-node cluster with 3-way replication

In this scenario, each range is replicated 3 times, with each replica on a different node:

Decommission Scenario 1

If you try to decommission a node, the process will hang indefinitely because the cluster cannot move the decommissioning node's replicas to the other 2 nodes, which already have a replica of each range:

Decommission Scenario 1

To successfully decommission a node in this cluster, you need to add a 4th node. The decommissioning process can then complete:

Decommission Scenario 1

5-node cluster with 3-way replication

In this scenario, like in the scenario above, each range is replicated 3 times, with each replica on a different node:

Decommission Scenario 1

If you decommission a node, the process will run successfully because the cluster will be able to move the node's replicas to other nodes without doubling up any range replicas:

Decommission Scenario 1

5-node cluster with 5-way replication for a specific table

In this scenario, a custom replication zone has been set to replicate a specific table 5 times (range 6), while all other data is replicated 3 times:

Decommission Scenario 1

If you try to decommission a node, the cluster will successfully rebalance all ranges but range 6. Since range 6 requires 5 replicas (based on the table-specific replication zone), and since CockroachDB will not allow more than a single replica of any range on a single node, the decommissioning process will hang indefinitely:

Decommission Scenario 1

To successfully decommission a node in this cluster, you need to add a 6th node. The decommissioning process can then complete:

Decommission Scenario 1

Remove a single node (live)

Before decommissioning a node

To ensure your cluster can adequately handle decommissioning nodes:

  • Before decommissioning each node verify that there are no underreplicated or unavailable ranges.
  • If you have a decommissioning node that appears to be hung, you can recommission the node. If you notice any issues persisting, contact our support team.

    If possible, keep the node running instead of stopping it, because a hung decommissioning process might be a symptom of a problem that could result in data loss.

  • Confirm that there are enough nodes to take over the replicas from the node you want to remove. See some Example scenarios above.

Step 1. Get the ID of the node to decommission

Open the Admin UI and scroll to the Node List on the Overview page. Note the ID of the node that you want to decommission (the ID is the number prepended by n):

Decommission a single live node

Step 2. Check the node before decommissioning

In the Admin UI, click Metrics on the left, select the Replication dashboard, and hover over the Replicas per Store and Leaseholders per Store graphs:

Decommission a single live node
Decommission a single live node

Step 3. Start the decommissioning process on the node

Run the cockroach node decommission command with the ID of the node to decommission:

copy

icon/buttons/copy

$ cockroach node decommission 4 --certs-dir=certs --host=<address of any live node>

copy

icon/buttons/copy

$ cockroach node decommission 4 --insecure --host=<address of any live node>

You'll then see the decommissioning status print to stderr as it changes:

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  true   |       45 |        true        |    false     
(1 row)

Once the node has completed the decommissioning process, you'll see a confirmation:

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  true   |        0 |        true        |    false     
(1 row)

No more data reported on target nodes. Please verify cluster health before removing the nodes.

Note that is_decommissioning will remain true after all replicas have been transferred from the node.

Step 4. Check the node and cluster after the decommissioning process

In the Admin UI Replication dashboard, again hover over the Replicas per Store and Leaseholders per Store graphs. For the decommissioning node, the counts should be 0:

Decommission a single live node
Decommission a single live node

Return to the Node List on the Overview page. The DECOMMISSIONING node should have 0 replicas, and all other nodes should be healthy (LIVE):

Decommission a single live node
Tip:

Even with zero replicas on a node, its status on the Node List will be DECOMMISSIONING until you stop the node. It is also counted as a "Suspect" node in the Cluster Overview panel until being shut down.

Step 5. Stop the decommissioning node

A node should be drained of SQL clients and distributed SQL queries before being shut down.

Run the cockroach node drain command with the address of the node to drain:

copy

icon/buttons/copy

cockroach node drain --certs-dir=certs --host=<address of node to drain>

copy

icon/buttons/copy

cockroach node drain --insecure --host=<address of node to drain>

Once the node has been drained, you'll see a confirmation:

node is draining... remaining: 1
node is draining... remaining: 0 (complete)
ok

Stop the node using one of the following methods:

  • If the node was started with a process manager like systemd, stop the node using the process manager. The process manager should be configured to send SIGTERM and then, after about 1 minute, SIGKILL.
  • If the node was started using cockroach start and is running in the foreground, press ctrl-c in the terminal.
  • If the node was started using cockroach start and the --background and --pid-file flags, run kill <pid>, where <pid> is the process ID of the node.

After the duration configured via server.time_until_store_dead, you'll see the stopped node listed under Recently Decommissioned Nodes:

Decommission a single live node

At this point, the node is DECOMMISSIONED and will no longer appear in timeseries graphs unless you view a time range during which the node was live. However, it will never disappear from the historical list of decommissioned nodes, linked beneath Recently Decommissioned Nodes.

Remove a single node (dead)

After a node has been dead for 5 minutes, CockroachDB transfers the range replicas and range leases on the node to available live nodes. However, if the dead node is restarted, the cluster will rebalance replicas and leases to the node.

To prevent the cluster from rebalancing data to a dead node if it comes back online, do the following:

Step 1. Get the ID of the dead node

Open the Admin UI and scroll to the Node List on the Overview page. Note the ID of the node listed as DEAD (the ID is the number prepended by n):

Decommission a single dead node

Step 2. Mark the dead node as decommissioned

Run the cockroach node decommission command with the ID of the node to officially decommission:

copy

icon/buttons/copy

$ cockroach node decommission 4 --certs-dir=certs --host=<address of any live node>

copy

icon/buttons/copy

$ cockroach node decommission 4 --insecure --host=<address of any live node>

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  false  |        0 |        true        |    true      
(1 row)

No more data reported on target nodes. Please verify cluster health before removing the nodes.

Within 5 minutes, you'll see the node move from the Node List to the Recently Decommissioned Nodes list, with the new status DECOMMISSIONED.

Decommission a single live node

At this point, the node is DECOMMISSIONED and will no longer appear in timeseries graphs unless you view a time range during which the node was live. However, it will never disappear from the historical list of decommissioned nodes, linked beneath Recently Decommissioned Nodes.

Note:

If you want to utilize a decommissioned node again, first recommission the node to have the cluster rebalance data to the node. Then restart the node so that it accepts new SQL connections.

Remove multiple nodes

Before decommissioning nodes

  • Before decommissioning each node verify that there are no underreplicated or unavailable ranges.
  • If you have a decommissioning node that appears to be hung, you can recommission the node. If you notice any issues persisting, contact our support team.

    If possible, keep the node running instead of stopping it, because a hung decommissioning process might be a symptom of a problem that could result in data loss.

  • Confirm that there are enough nodes to take over the replicas from the node you want to remove. See some Example scenarios above.

Step 1. Get the IDs of the nodes to decommission

Open the Admin UI and scroll to the Node List on the Overview page. Note the IDs of the nodes that you want to decommission (the ID is the number prepended by n):

Decommission multiple nodes

Step 2. Check the nodes before decommissioning

In the Admin UI, click Metrics on the left, select the Replication dashboard, and hover over the Replicas per Store and Leaseholders per Store graphs:

Decommission multiple nodes
Decommission multiple nodes

Step 3. Start the decommissioning process on the nodes

Run the cockroach node decommission command with the IDs of the nodes to decommission:

copy

icon/buttons/copy

$ cockroach node decommission 4 5 --certs-dir=certs --host=<address of any live node>

copy

icon/buttons/copy

$ cockroach node decommission 4 5 --insecure --host=<address of any live node>

You'll then see the decommissioning status print to stderr as it changes:

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  true   |       18 |        true        |    false     
  5 |  true   |       16 |        true        |    false     
(2 rows)

Once the nodes have been fully decommissioned, you'll see a confirmation:

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  true   |        0 |        true        |    false     
  5 |  true   |        0 |        true        |    false     
(2 rows)

No more data reported on target nodes. Please verify cluster health before removing the nodes.

Note that is_decommissioning will remain true after all replicas have been transferred from each node.

Step 4. Check the nodes and cluster after the decommissioning process

In the Admin UI Replication dashboard, again hover over the Replicas per Store and Leaseholders per Store graphs. For the decommissioning nodes, the counts should be 0:

Decommission multiple nodes
Decommission multiple nodes

Return to the Node List on the Overview page. The DECOMMISSIONING nodes should each have 0 replicas, and all other nodes should be healthy (LIVE):

Decommission multiple nodes
Tip:

Even with zero replicas on a node, its status on the Node List will be DECOMMISSIONING until you stop the node. It is also counted as a "Suspect" node in the Cluster Overview panel until being shut down.

Step 5. Stop the decommissioning nodes

Nodes should be drained of SQL clients and distributed SQL queries before being shut down.

For each node, run the cockroach node drain command with the address of the node to drain:

copy

icon/buttons/copy

cockroach node drain --certs-dir=certs --host=<address of node to drain>

copy

icon/buttons/copy

cockroach node drain --insecure --host=<address of node to drain>

Once each node has been drained, you'll see a confirmation:

node is draining... remaining: 1
node is draining... remaining: 0 (complete)
ok

Stop each node using one of the following methods:

  • If the node was started with a process manager like systemd, stop the node using the process manager. The process manager should be configured to send SIGTERM and then, after about 1 minute, SIGKILL.
  • If the node was started using cockroach start and is running in the foreground, press ctrl-c in the terminal.
  • If the node was started using cockroach start and the --background and --pid-file flags, run kill <pid>, where <pid> is the process ID of the node.

After the duration configured via server.time_until_store_dead, you'll see the stopped nodes listed under Recently Decommissioned Nodes:

Decommission multiple nodes

At this point, the nodes are DECOMMISSIONED and will no longer appear in timeseries graphs unless you view a time range during which the nodes were live. However, they will never disappear from the historical list of decommissioned nodes, linked beneath Recently Decommissioned Nodes.

Note:

If you want to utilize a decommissioned node again, first recommission the node to have the cluster rebalance data to the node. Then restart the node so that it accepts new SQL connections.

Recommission nodes

If you accidentally started decommissioning a node, or have a node with a hung decommissioning process, you can recommission the node. This cancels the process of transferring replicas on the node to other nodes.

Note:

Recommissioning is intended to cancel an active decommissioning process. If all ranges have been removed from a node, start a new node instead of reusing the node.

Step 1. Cancel the decommissioning process

Press ctrl-c in each terminal with an ongoing decommissioning process that you want to cancel.

Step 2. Recommission the decommissioning nodes

Execute the cockroach node recommission command with the IDs of the nodes to recommission:

copy

icon/buttons/copy

$ cockroach node recommission 4 --certs-dir=certs --host=<address of any live node>

copy

icon/buttons/copy

$ cockroach node recommission 4 --insecure --host=<address of any live node>

The value of is_decommissioning will change back to false:

 id | is_live | replicas | is_decommissioning | is_draining  
+---+---------+----------+--------------------+-------------+
  4 |  false  |        0 |       false        |    false      
(1 row)

On the Node List, you should soon see the recommissioned nodes listed as LIVE. After a few minutes, you should see replicas rebalanced to the nodes.

Check the status of decommissioning nodes

To check the progress of decommissioning nodes, run the cockroach node status command with the --decommission flag:


copy

icon/buttons/copy

$ cockroach node status --decommission --certs-dir=certs --host=<address of any live node>

copy

icon/buttons/copy

$ cockroach node status --decommission --insecure --host=<address of any live node>

 id |        address         |  build  |            started_at            |            updated_at            | is_available | is_live | gossiped_replicas | is_decommissioning | is_draining  
+---+------------------------+---------+----------------------------------+----------------------------------+--------------+---------+-------------------+--------------------+-------------+
  1 | 165.227.60.76:26257    | 91a299d | 2018-10-01 16:53:10.946245+00:00 | 2018-10-02 14:04:39.280249+00:00 |         true |  true   |                26 |       false        |    false     
  2 | 192.241.239.201:26257  | 91a299d | 2018-10-01 16:53:24.22346+00:00  | 2018-10-02 14:04:39.415235+00:00 |         true |  true   |                26 |       false        |    false     
  3 | 67.207.91.36:26257     | 91a299d | 2018-10-01 17:34:21.041926+00:00 | 2018-10-02 14:04:39.233882+00:00 |         true |  true   |                25 |       false        |    false     
  4 | 138.197.12.74:26257    | 91a299d | 2018-10-01 17:09:11.734093+00:00 | 2018-10-02 14:04:37.558204+00:00 |         true |  true   |                25 |       false        |    false     
  5 | 174.138.50.192:26257   | 91a299d | 2018-10-01 17:14:01.480725+00:00 | 2018-10-02 14:04:39.293121+00:00 |         true |  true   |                 0 |        true        |    false          
(5 rows)
  • is_decommissioning == true implies that replicas are being or have been transferred to other nodes. The node is either undergoing or has completed the decommissioning process.
  • is_draining == true implies that the node is no longer accepting SQL connections. The node is either in the process of shutting down or has already done so.

See also



Yes No