Constraints and Limits

Before using EMR, carefully read and understand the following use limits:
To ensure the cluster network security, new clusters will be placed in the same VPC. Do not change the VPC of an existing cluster or node; otherwise, the cluster network may fail.
When you create a cluster, EMR can help you create a new security group, or you can also manually select an existing EMR security group. Make sure that the selected security group has the necessary inbound/outbound rules for EMR. Do not delete or change the security group in use after creating the cluster; otherwise, cluster communication may fail, thus affecting the service.
Plan the storage space of nodes in advance based on your business needs, and promptly add storage nodes, as an insufficient storage space may cause data and node risks. Currently, core, task, and router nodes in the EMR cluster support mounting multiple cloud disks, and a node can have up to 15 cloud disks. Clusters in BM 2.0 and local disk models (IO and D series) don't support mounting multiple cloud disks.
When using EMR, do not perform operations in the CVM console, such as shutdown, restart, VPC switch, security group rule adjustment, so as to avoid cluster exceptions. OS reinstallation, instance termination, configuration adjustment, renewal, and billing mode change are also not recommended. You can perform necessary cluster maintenance operations in the EMR console.
Public IPs can increase the possibility of master nodes being attacked, so you need to manage and monitor the risks. EIPs (including the IPs on the secondary ENI) will be retained after the cluster is terminated, and the idle IPs will continue to incur fees. If you don't need to retain them, release them on the corresponding resource management page.
When you create a cluster, EMR provides component initialization parameters for general scenarios. Before you use components such as HDFS and HBase, we recommend you check whether the component parameters meet the needs of your business scenarios. To get the component initialization guide, contact us.
Keep the host login password of your EMR cluster secure. If you configure passwordless login for cross-node access, Tencent Cloud security services may detect vulnerability risks and prompt you.
Even if an exception occurs in your cluster, the cluster will continue to be billed. In this case, we recommend you promptly contact us for assistance. If we need to log in to your cluster for troubleshooting, we will gain your consent to request your account and password.
When you use or maintain your EMR cluster, some unexpected operations may render it unavailable or unstable, and you will receive a risk warning before performing such operations in the console. This document lists some of the prohibited and risky operations:
Prohibited Operations
Operation
Risk
Change the private IP of an EMR node in CVM
Node communication exception or cluster unavailability
Modify the security group of a CVM node while the cluster is running
Node communication exception or component service unavailability
Delete an existing process, application, or file from a node
Cluster/Component service unavailability
Delete or modify the `hosts` file in the `/etc` directory
Service exception, as the cluster cannot be associated with the service on the node
Delete or modify the HDFS metadata file `edit log`
HDFS cluster unavailability
Manually modify the data in the Hive metadatabase
Service exception caused by a Hive data parsing error
Delete a ZooKeeper data directory
Failure of dependent components
Risky Operations
Operation
Risk
Suggestion
Shut down or restart an EMR cluster node in CVM
Service unavailability
Check whether the operation is necessary and read the CVM operation limits
Mount a disk to an EMR node in the CVM console
Disk unavailability caused by EMR's failure to recognize and initialize the disk
Do this through core node scaling or under technical guidance
Unmount a disk from an EMR node in the CVM console
Data loss or cluster unavailability
Do this through core node scaling or under technical guidance
Modify the component configuration file parameters in CVM
Modified parameter overwrite after service restart
Modify the parameter configuration in the EMR console and seek technical guidance in special circumstances
Delete or modify the `resolv.conf` file in the `/etc` directory
Service exception, as the cluster cannot be associated with the service on the node
Check whether the operation is necessary and perform it under technical guidance
Modify the MetaDB password
EMR depends on the password configured in MetaDB, and after the password is changed, services such as Hive and Ranger will become unavailable
Modify the configuration in the EMR console under technical guidance
Modify the MetaDB floating IP
Hive and Ranger service unavailability, as EMR depends on the IP configured in MetaDB
Modify the configuration in the EMR console under technical guidance
Modify the MetaDB security group
Interruption of the communication between MetaDB and the cluster, or Hive and Ranger service unavailability
Perform the operation under technical guidance
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Operation	Risk
Change the private IP of an EMR node in CVM	Node communication exception or cluster unavailability
Modify the security group of a CVM node while the cluster is running	Node communication exception or component service unavailability
Delete an existing process, application, or file from a node	Cluster/Component service unavailability
Delete or modify the `hosts` file in the `/etc` directory	Service exception, as the cluster cannot be associated with the service on the node
Delete or modify the HDFS metadata file `edit log`	HDFS cluster unavailability
Manually modify the data in the Hive metadatabase	Service exception caused by a Hive data parsing error
Delete a ZooKeeper data directory	Failure of dependent components

Operation	Risk	Suggestion
Shut down or restart an EMR cluster node in CVM	Service unavailability	Check whether the operation is necessary and read the CVM operation limits
Mount a disk to an EMR node in the CVM console	Disk unavailability caused by EMR's failure to recognize and initialize the disk	Do this through core node scaling or under technical guidance
Unmount a disk from an EMR node in the CVM console	Data loss or cluster unavailability	Do this through core node scaling or under technical guidance
Modify the component configuration file parameters in CVM	Modified parameter overwrite after service restart	Modify the parameter configuration in the EMR console and seek technical guidance in special circumstances
Delete or modify the `resolv.conf` file in the `/etc` directory	Service exception, as the cluster cannot be associated with the service on the node	Check whether the operation is necessary and perform it under technical guidance
Modify the MetaDB password	EMR depends on the password configured in MetaDB, and after the password is changed, services such as Hive and Ranger will become unavailable	Modify the configuration in the EMR console under technical guidance
Modify the MetaDB floating IP	Hive and Ranger service unavailability, as EMR depends on the IP configured in MetaDB	Modify the configuration in the EMR console under technical guidance
Modify the MetaDB security group	Interruption of the communication between MetaDB and the cluster, or Hive and Ranger service unavailability	Perform the operation under technical guidance

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