atomic host upgrade- this command, in turn, leverages the
rpm-ostreetooling to download ostree layers from a repository managed by Red Hat. It’s worth noting that only the file-level delta between the running ostree and the upgrade are transferred. This is incredibly efficient from a network perspective and beneficial for minimizing bandwidth usage for disperse systems. When you upgrade, the latest ostree is made available and then deployed the next time you reboot. By default, the system keeps the newest two ostree layers locally downloaded and if there is an emergency in your cluster, you can use the
atomic host rollbackcommand to recover. Adding Software RHEL Atomic Host is designed to fit nicely into an immutable infrastructure - it provides an immutable host maintained and updated by Red Hat. Many of the tools you might want to use might not be part of the ostree - that’s ok, because this allows developers, architects, and systems administrators to focus on adding software through containers. Containerizing additional needed software keeps the system lean and manageable. However, there are a few options which provide flexibility to Atomic - Super-Privileged Containers and package layering . The Super-Privileged Containers can access the host in order to monitor or troubleshoot the host. The RHEL Atomic Tools container is provided by Red Hat and has many debugging tools like sosreport, traceroute, strace, tcpdump. As a fallback for software that is difficult to put in a container, RHEL Atomic Host has something called package layering. Using the atomic host install [rpms] command lets you install packages that are not part of the original ostree. Dependencies are automatically resolved for these packages and during ostree upgrades, the system will check for updates for these packages in one operation. Layered packages persist across upgrades of the host (and package updates are checked at host upgrade time). Preinstalled Tools
- RHEL Atomic Host comes pre-installed with all the tools for running containers - docker, runc, kubernetes client, etcd, flannel, atomic. Orchestrating containers via Kubernetes is supported in a single master/node deployment on a single system. Larger, multi-system environments use OpenShift Container Platform to provide multi-host, container orchestration. Additional details about supported container orchestration tools can be found at How are container orchestration tools supported with Red Hat Enterprise Linux?.
- RHEL Atomic Host has comes pre-installed with container performance tuning profiles, Ceph & Gluster storage clients, SSSD, and iSCSI tools.
The operating system content is delivered as an immutable ostree. Any additional software not found in the ostree should be run from inside of a container. This may require the use of the
--privilegeddocker option or a Super-Privileged Container such as the RHEL Atomic Tools container for software that cannot be run from a container.
yumcommand is not present in RHEL Atomic Host and cannot be used to install packages. However, it is still possible to use the
rpmcommand to query packages installed in the immutable ostree. Note that Yum is available inside RHEL-based container images.
As a fall back, it is possible to install RPMs on the system using the
atomic installcommand. This is highly useful for troubleshooting a system that is misbehaving.
- RHEL Atomic Host supports atomic upgrades and rollbacks of the OS. You can power off the system during an upgrade/rollback operation and it will still be functional during the next boot. RHEL Server is not as fault-tolerant during upgrades and does not have robust rollback support. This is useful in large distributed systems.
On RHEL Atomic Host, there are two new directories in root (
/sysroot/directory, and the
atomic host deploycommand is available on Atomic Host which lets you choose a specific version of an ostree, bringing more flexibility than upgrade and rollback. For example, you can the following command to deploy a particular version of RHEL Atomic Host:
# atomic host deploy 7.2.7
No man pages - To save storage space, manual pages are not shipped with the Atomic Host image. However, the RHEL Atomic Tools container has the man pages for the packages that make up the ostree and you can access them by running the container:
# atomic run rhel7/rhel-tools man rpm-ostree
- Cockpit is a powerful, modern web UI for RHEL and RHEL Atomic Host. The web frontend is delivered as a container for Atomic Host and provides an interface that makes administering containers a breeze for admins who come from a virtualization background.
- From the boot prompt, Atomic Host has the ability to go straight into the Cockpit UI via Developer Mode. This provides developers with configuration free access to get started with containers. See Chapter 2 of the Red Hat Enterprise Linux Atomic Host 7 Installation and Configuration Guide for additional information about Developer Mode.
There are only two writable directories for local system configuration:
/var/. All other directories on the system are read-only. User and host specific data that is intended to persist across updates should be stored only in the
/var/directory. For example, the
/homedirectory is symlinked to
/var/homeand therefore is writable as usual. Configuration files in the
/etc/directory can still be modified as usual.'
- The storage configuration of RHEL Atomic Host uses LVM by default. During installation, two Logical Volumes (LV) are created. The root LV is used for the operating system content. The "docker-pool" LV is thinly-provisioned and is configured to grow automatically. The "docker-pool" LV is used as the storage backend for Docker. The Docker storage configuration is managed via the atomic CLI and/or Cockpit.
- RHEL Atomic Host provides a choice between docker and docker-latest, but Red Hat does not support running both docker and docker-latest on the same machine at the same time.
- There are two new tuned profiles optimized for Atomic, atomic-host for physical machines and atomic-guest for virtual machines.
atomic scancommand is available on both systems (on RHEL Atomic Host it is pre-installed) to check if your containers comply with the security policies, and if they have vulnerabilities. Support - RHEL Atomic Host is included with RHEL Server subscriptions at no extra cost. End users can gain access to support through phone or the Red Hat portal with the same level of support as RHEL Server. Same RPMs - RHEL Atomic Host is built using a subset of the exact same RPMs that are used in RHEL Server, however their content is delivered in the form of an immutable ostree. This allows administrators to leverage their RHEL knowledge but still gain the manageability of an immutable system in a large distributed system. I Want To Run Containers. How do I know which RHEL I need? If you want to build containers - RHEL Server or RHEL Atomic Host
If you want full-blown build environment - CDK, RHEL Server If you want to run containers in production in a large distributed system - RHEL Atomic Host
If you want to run containers in production, but can’t add another operating system variant - RHEL Server
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