Page last updated: This topic describes the components used to ensure high availability in Cloud Foundry, vertical and horizontal scaling, and the infrastructure required to support scaling component VMs for high availability. Components of a High Availability Deployment This section describes the system components needed to ensure high availability. Availability Zones During product updates and platform upgrades, the VMs in a deployment restart in succession, rendering them temporarily unavailable. During outages, VMs go down in a less orderly way. Spreading components across Availability Zones (AZs) and scaling them to a sufficient level of redundancy maintains high availability during both upgrades and outages and can ensure zero downtime. Deploying Cloud Foundry across three or more AZs and assigning multiple component instances to different AZ locations lets a deployment operate uninterrupted when entire AZs become unavailable. Cloud Foundry maintains its availability as long as a majority of the AZs remain accessible.

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For example, a three-AZ deployment stays up when one entire AZ goes down, and a five-AZ deployment can withstand an outage of up to two AZs with no impact on uptime. External Load Balancers Production environments should use a highly-available customer-provided load balancing solution that does the following: • Provides load balancing to each of the Cloud Foundry Router IP addresses • Supports SSL termination with wildcard DNS location • Adds appropriate x-forwarded-for and x-forwarded-proto HTTP headers to incoming requests • (Optional) Supports WebSockets If you are deploying in lab and test environments, the use-haproxy.yml ops file enables HAProxy for your foundation.

Blob Storage For storing blobs, large binary files, the best approach for high availability is to use external storage such as Amazon S3 or an S3-compatible service. If you store blobs internally using WebDAV or NFS, these components run as single instances and you cannot scale them. For these deployments, use the high availability features of your IaaS to immediately recover your WebDAV or NFS server VM if it fails. Contact if you need assistance. The singleton compilation components do not affect platform availability. Vertical and Horizontal Scaling for High Availability You can scale platform capacity vertically by adding memory and disk, or horizontally by adding more VMs running instances of Cloud Foundry components. The nature of the applications you host on Cloud Foundry should determine whether you should scale vertically or horizontally.

For more information about scaling applications and maintaining app uptime, see. Scale Vertically Scaling vertically means adding memory and disk to your component VMs. To scale vertically, ensure that you allocate and maintain enough of the following: • Free space on host Diego cell VMs so that apps expected to deploy can successfully be staged and run. • Disk space and memory in your deployment such that if one host VM is down, all instances of apps can be placed on the remaining Host VMs.

• Free space to handle one AZ going down if deploying in multiple AZs. Scale Horizontally Scaling horizontally means increasing the number of VM instances dedicated to running a functional component of the system. You can horizontally scale most Cloud Foundry components to multiple instances to achieve the redundancy required for high availability. You should also distribute the instances of multiply-scaled components across different AZs to minimize downtime during ongoing operation, product updates, and platform upgrades. If you use more than three AZs, ensure that you use an odd number of AZs. For more information regarding zero downtime deployment, see.

The following table provides recommended instance counts for a high-availability deployment and the minimum instances for a functional deployment: Pivotal Application Service (PAS) Job Recommended Instance Number for HA Minimum Instance Number Notes Diego Cell ≥ 3 1 The optimal balance between CPU/memory sizing and instance count depends on the performance characteristics of the apps that run on Diego cells. Scaling vertically with larger Diego cells makes for larger points of failure, and more apps go down when a cell fails.

On the other hand, scaling horizontally decreases the speed at which the system rebalances apps. Rebalancing 100 cells takes longer and demands more processing overhead than rebalancing 20 cells. Diego Brain ≥ 2 1 For high availability, use at least one per AZ, or at least two if only one AZ. Diego BBS ≥ 2 1 For high availability in a multi-AZ deployment, use at least one instance per AZ. Scale Diego BBS to at least two instances for high availability in a single-AZ deployment. Consul ≥ 3 1 Set this to an odd number equal to or one greater than the number of AZs you have, in order to maintain quorum.