September 30th, 2021

Machine translation is used partially for this article. See the Japanese version for the original article.

Introduction

In Oracle Cloud Infrastructure (hereinafter called "OCI"), we tried building an HA cluster using EXPRESSCLUSTER.

EXPRESSCLUSTER can make redundant instances (Compute instances in OCI) provided in cloud environments.
Click here for the EXPRESSCLUSTER Setup Guides in the cloud environment.

Also OCI's Block Volume released multi-attach features that can be attached to multiple Compute instances, allowing EXPRESSCLUSTER X to build shared disk type HA clusters.
This time, we will build a shared disk type HA cluster using block volume's multi-attach features.

Contents

1. Configuration of HA Cluster Environment on OCI

In EXPRESSCLUSTER X 4.2 or later, Oracle Cloud virtual IP resources (hereinafter called "ocvip") as a dedicated resource for OCI have been available, make it easier to build HA cluster on OCI.
Ocvip allows clients to continue their work without being aware of switching instances in the event of a failover or group move.

2. What is Block Volume Multi-Attach Features?

Block Volume's multi-attach feature allows you to attach a block volume to multiple Compute instances.

Previously, it could not be treated as a disk connected to multiple Compute instances, such as a shared disk.
From now on, however, Block Volume's multi-attach features allows block volumes to be treated like shared disks.
EXPRESSCLUSTER X shared disk clusters are an option in environments where I/O performance is important because there is no write performance degradation associated with synchronizing I/O data, such as mirror disk clusters.

Block Volume's multi-attach features provides these benefits, but the application must maintain the write order to ensure that the data in block volume is consistent.
If you write data from multiple Compute instances without controlling the write, the data may appear to be written successfully at first glance, but it may actually be destroying the file system.
Therefore, it is necessary to take measures such as controlling instances that can write data, such as EXPRESSCLUSTER X disk resources (shared disk control resources).

3. Shared Disk Type HA Cluster Configuration

In this case, we built a "shared disk type HA cluster" in the Ashburn region environment, and confirmed that block volumes attached to multiple instances can be controlled by disk resources.

In this configuration, a two-node shared disk type HA cluster is built, and the instance that can access block volume with multi-attach features enabled is switched by the disk resource that controls the shared disk.

The configuration is as follows:

Block Volume is attached to both nodes, but is accessible only from the nodes where disk resources are running (the active server in the case of figure) due to disk resource control.
Block Volume cannot be referenced or written from the standby server.

If the active server fails, the standby server starts the disk resource and can reference and write block volume from the standby server.

By specifying a virtual IP address that ocvip control to access business applications, the client can access to the cluster without being aware of which node is running.

4. Procedure for Building a Shared Disk Type HA Cluster

For detailed instructions, see the HA Cluster Configuration Guide.

Conclusion

In this case, we tried to build a shared disk type HA cluster using block volume multi-attach features in OCI.
If you have a request to build a shared disk type HA cluster on OCI, please try it.

If you consider introducing the configuration described in this article, you can perform a validation with the trial module of EXPRESSCLUSTER. Please do not hesitate to contact us if you have any questions.