Node Status & Actions
Each node in a universe has a Status column indicating its current logical state as per the YugaWare layer. This section first describes what each of them means and gives information on when and how these can be modified by the user. The nodes tab on the universe page shows them. When we create a universe, the
Nodes tab on the universe page provides the phyiscal (such as ip, cloud) and the logical state information (master, status etc) about that node. Note that the
STATUS for each node is
Live. This is the steady state value for a normally functioning node.
The current list of status columns and some related information.
|To Be Added||The backing instance for this node is being created on the IaaS.|
|Live||Steady state default status of a healthy node. All the server processes are running on that node.|
|Stopped||Server processes (yb-tserver and yb-master, if applicable) on that node have been stopped.|
|Removed||The node does not have any more data and the server processes have been stopped. It is not participating in the universe.|
|Decommissioned||The underlying instance has been released to the IaaS. This can happen only after a node is removed or processes stopped.|
|Provisioned||During universe (or cluster) creation, this indicates the instance is being setup with the required OS packages (for ex. ntp, chronyd).|
|Software Installed||During universe (or cluster) creation, this indicates YugaByte software is being deployed on this node.|
|Upgrade Software||The software version is being updated on this node and the master/tserver processes will be restarted.|
|Upgrade GFlags||A server (master or tserver) process config file is being updated and the corresponding server will be restarted.|
|Unreachable||YugaWare is not able to get information from the node_exporter process on that node.|
|Destroyed||Very transient, while the universe (or cluster) is being deleted.|
For some of node statuses, there are some actions that are allowed to help make changes to that nodes’ backing IaaS instance. They provide a way to handle errors per node and seamlessly take care of data migration in case of instance failures and load balancing in case of node addition.
|To Be Added||Delete||This action can be taken if a universe create fails and node is stuck in ‘To Be Added’. Once this action is performed, the node (and its underlying instance) will be removed from this universe.|
|Live||Stop Processes, Remove Node||The server processes on the node will be stopped, node status becomes ‘Stopped’. A Live node can be also marked as ‘Removed’, which moves the data out of it along with stopping the server processes running on that node. Note that the backing instance is still under the control of the universe. This removes the MASTER/TSERVER setting of the node on the UI.|
|Stopped||Start Processes, Release Instance||The server processes that are stopped on that node can be restarted using the ‘Start Processes’ pulldown option. The other option for a ‘Stopped’ node is to release the backing instance to IaaS and that will stop tracking the ip of this node in the universe.|
|Removed||Add Node, Release Instance||A removed node can be added back - this restarts the processes on that node and move data onto it from other nodes, and marks it ‘Live’. The other option is to release the backing instance to IaaS, and this will stop tracking the ip of this node in the universe and the node will be marked ‘Decomissioned’.|
|Decommissioned||Add Node||A new instance will be used/spawned to replace the released instance, server processes restarted and data load balanced onto this node. It will become ‘lIve’ after this operation.|
Rest of the status types do not have any user actions, as they are mostly transient and will end up in one of the above statuses.
NoteAdd Node just recreates a new backing instance for an existing node in the universe/cluster. To add a completely new node (as in, increase the number of nodes in the universe), one can use the ‘Edit Universe’ option to expand the universe.
The rest of this page describes how to modify the state of each node in a universe/cluster. The UI provides different actions that can be taken against each node under the
ACTION column drop down.
There are two broad set of use cases:
Long duration operations needing removal of underlying instance
Following are the steps to ensure that an underlying instance for a given node can be replaced with a new instance without any data loss.
Removal of an instance that is dying
Let’s say, for example, that a VM/machine in the universe is hitting end of life or having unrecoverable hardware or other system (OS, disk etc) problems. The machine crashes for good, and so there are no processes running on it. This will be detected by the UI and shown as an
Unreachable node. Note that RAFT will ensure other leaders will get elected for the underlying data shards. But the universe is in an partial under replicated scenario and will not be able to tolerate many more failures. So quick remedy is needed.
So, for the
yb-14-node-actions-n3 node, one can use the dropdown
Actions at the end and choose the
Remove Node option. This will bring the node to the
Removed status and no further data can be accessed on this node (as the server processes are shutdown).
Note that there is no
MASTER/TSERVER shown for that node. If that node was the
Master Leader, then the RAFT level election will move it to another node quickly. Similar leader elections happen for tablets for which this node was the the leader tablet server.
Since we know that the instance is dead, we can go ahead and release the ip as well using the ‘Release Instance’ dropdown option at the end of the Removed node. It will show up as a
The node can brought back to life on a new backing instance using the
Add Node option from the dropdown for the
Decomissioned node. For IaaS, like AWS and GCP, YugaWare will spawn with the existing instance type in the correct/existing region and zone of that node. After the end of this operation, the node will have yb-master/yb-tserver processes running along with some data that is load balanced onto this node and status will be marked ‘Live’. Note that the node name is reused and is part of the healthy cluster now.
REMOVEmore than (RF - 1)/2 nodes at any given time. For example, on a RF=3 cluster with 3 server nodes, there can only be one removed node. This is needed for RAFT consensus algorithm. We will be adding safeguards against this soon.
REMOVE NODEwill not work for the case where the number of nodes is equal to the RF of the cluster. Since there is no other nodes to move the data via the load balancer.
Quick operations, on an existing instance
The second scenario is for more of a ‘quick’ planned change that can be performed on a node. For example, the DevOps wants to mount a new disk on the node or just install and run a new security daemon. In that case, the instance is still in use and stopping any running YugaByte process might be needed. Then the user can pick the
Stop Processes option and then perform the system task, and then pick the
Start Processes for that node.
The following two steps helps stop the server processes on the node and restart it back up. There is no data moved out of the node proactively, but the data shard/tablet leaders could change as perf RAFT requirements.
yb-14-node-actions-n4 is the node that needs the intervention, then one would pick the ‘Stop Processes’ option.
Once the yb-tserver (and yb-master, if applicable) are stopped, the node status is updated and the instance is ready for the planned system changes.
NoteDo not STOP more than (RF - 1)/2 processes at any given time. For example, on an RF=3 cluster with 3 nodes, there can only be one node with stopped processes to allow majority of nodes to perform consensus operations.
After the work is complete, the processes can be restarted via the same dropdown for that node.
The node will go back to ‘Live’ state once the processes are up and running.
In the worst case scenario, when the system runs into some unrecoverable errors at this stage, there is a
Release Instance option for the stopped node, which will help remove the backing instance as well, as decribed above.
Node Action Task Summary
As a summary of all the actions that were run on this universe, one can check the ‘Tasks’ tab to see the remove/add and stop/start tasks that were run on that universe.