kubespray/docs/advanced/downloads.md

Downloading binaries and containers

Kubespray supports several download/upload modes. The default is:

• Each node downloads binaries and container images on its own, which is download_run_once: False.
• For K8s apps, pull policy is k8s_image_pull_policy: IfNotPresent.
• For system managed containers, like kubelet or etcd, pull policy is download_always_pull: False, which is pull if only the wanted repo and tag/sha256 digest differs from that the host has.

There is also a "pull once, push many" mode as well:

• Setting download_run_once: True will make kubespray download container images and binaries only once and then push them to the cluster nodes. The default download delegate node is the first kube_control_plane.
• Set download_localhost: True to make localhost the download delegate. This can be useful if cluster nodes cannot access external addresses. To use this requires that the container runtime is installed and running on the Ansible master and that the current user is either in the docker group or can do passwordless sudo, to be able to use the container runtime. Note: even if download_localhost is false, files will still be copied to the Ansible server (local host) from the delegated download node, and then distributed from the Ansible server to all cluster nodes.

NOTE: When download_run_once is true and download_localhost is false, all downloads will be done on the delegate node, including downloads for container images that are not required on that node. As a consequence, the storage required on that node will probably be more than if download_run_once was false, because all images will be loaded into the storage of the container runtime on that node, instead of just the images required for that node.

On caching:

• When download_run_once is True, all downloaded files will be cached locally in download_cache_dir, which defaults to /tmp/kubespray_cache. On subsequent provisioning runs, this local cache will be used to provision the nodes, minimizing bandwidth usage and improving provisioning time. Expect about 800MB of disk space to be used on the ansible node for the cache. Disk space required for the image cache on the kubernetes nodes is a much as is needed for the largest image, which is currently slightly less than 150MB.
• By default, if download_run_once is false, kubespray will not retrieve the downloaded images and files from the download delegate node to the local cache, or use that cache to pre-provision those nodes. If you have a full cache with container images and files and you don’t need to download anything, but want to use a cache - set download_force_cache to True.
• By default, cached images that are used to pre-provision the remote nodes will be deleted from the remote nodes after use, to save disk space. Setting download_keep_remote_cache will prevent the files from being deleted. This can be useful while developing kubespray, as it can decrease provisioning times. As a consequence, the required storage for images on the remote nodes will increase from 150MB to about 550MB, which is currently the combined size of all required container images.

Container images and binary files are described by the vars like foo_version, foo_download_url, foo_checksum for binaries and foo_image_repo, foo_image_tag or optional foo_digest_checksum for containers.

Container images may be defined by its repo and tag, for example: andyshinn/dnsmasq:2.72. Or by repo and tag and sha256 digest: andyshinn/dnsmasq@sha256:7c883354f6ea9876d176fe1d30132515478b2859d6fc0cbf9223ffdc09168193.

Note, the SHA256 digest and the image tag must be both specified and correspond to each other. The given example above is represented by the following vars:

dnsmasq_digest_checksum: 7c883354f6ea9876d176fe1d30132515478b2859d6fc0cbf9223ffdc09168193
dnsmasq_image_repo: andyshinn/dnsmasq
dnsmasq_image_tag: '2.72'

The full list of available vars may be found in the download's ansible role defaults. Those also allow to specify custom urls and local repositories for binaries and container images as well. See also the DNS stack docs for the related intranet configuration, so the hosts can resolve those urls and repos.