Scheduled Caching FAQs

isit the links below to download a version of the Orka CLI binary that matches your environment.

FAQ	Answer
Does caching have an impact on running VMs?	Caching small images (16GB) may be unnoticeable in VMs with long-running build times. (If a build takes 10 minute, then a cache operation of 1 minute has a lower impact on the overall duration of the build job). The greater the number of images cached, the more significant the impact on a running VM on that node, due to resource contention. The image caching operation consumes resources on the node, particularly disk I/O operations. The feature is referred to as Scheduled Caching, and the reason that caching operations should be strategically scheduled at opportune times to avoid resource contention on nodes in the Orka cluster with active CI jobs.
How many cache operations can run at once?	Currently, a cache job requires 0.5 CPU to run. On a machine with 8 CPU available, it can run a maximum of 16 jobs. Caching more images simultaneously is a faster process than caching multiple images sequentially.
Does caching have an impact on build performance?	Performance is impacted depending on the number of cache operations running. MacStadium recommends that build jobs and caching operations not run concurrently unless: - The actual image size (full image size) is small. - Long running builds are active and a caching performance hit is not a significant factor to job completion. - Other reasons you may be ok with a small performance drop while a build job is running.
OCI vs NFS caching - which one is better?	Pulling an image from a registry over the public internet is not as performant or reliable as pulling from the SAN in the same DC, which is why MacStadium recommends NFS. NFS cache operations are extremely consistent and predictable - running one operation on the same type of node under the same conditions provides the same result.
Does caching have an impact on the performance of other cache operations?	Yes. A VM running on a node with an active caching job has a noticeable increase in task execution time. This impact is proportional to the image size writing to cache.
Does caching have an impact on network, memory, or CPU performance?	Nodes with an active caching download impact a VM and its performance running processes including impacting network I/O operations.
Does caching have an impact on cluster performance?	The Orka scheduler can experience latency on the node member that has active caching operations.
OCI vs NFS caching - which one is better?	Pulling an image from a registry over the public internet is typically not as performant or reliable as pulling from the SAN in the same DC, which is why MacStadium recommends caching from NFS, or Orka’s local registry. NFS cache operations are extremely consistent and predictable - running one operation on the same type of node under the same conditions provides the same result.
Can I delete images from a cluster node cache?	Orka Cluster node cache image management, other than adding images, is performed automatically by the Orka Kubernetes control plane so there is no remove command in the image caching feature. To update an existing image simply cache a new copy of the image using the same name, or provide a relevant OCI image tag.