How OpenStack uses Ceph for storage
Ceph is often deployed with OpenStack as a back-end storage method. These two open source projects work together to make a well-integrated and robust solution for infrastructure.
OpenStack is an open source Infrastructure-as-a-Service (IaaS) platform that can provide public and private clouds in your datacenter or on the edge. OpenStack contains multiple projects; the most commonly installed are Nova (compute), Keystone (identity), Neutron (networking), Glance (image), Cinder (block storage), and Swift (object storage).
Ceph is an open source project that provides software-defined storage with unified (object, block, and file) storage. You can scale out this storage, and it is self-healing with the ability to anticipate failures.
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How Ceph and OpenStack work together
Ceph Storage Clusters, which are based on Reliable Autonomic Distributed Object Store (RADOS), can provide back-end storage for OpenStack. This image shows how they work together.
OpenStack's Keystone and Swift take advantage of Ceph by using the Ceph Object Gateway (a RADOS Rest Gateway, or RGW). This integration with Keystone allows the gateway to accept Keystone tokens for validation. This same gateway enables Swift to store its objects within Ceph.
On the other hand, Cinder, Glance, and Nova utilize Ceph block devices (RADOS block devices, or RBDs) for their back-end storage needs. Glance stores its images within Ceph, building virtual machines (VMs). Block storage devices created within Cinder for these VMs are provisioned within Ceph. And finally, Nova stores the virtual disk images of the running VMs within Ceph.
Open source makes it possible for these projects to integrate smoothly now and to maintain and improve their integration over time.
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The following resources are a good place to start to learn more about Ceph and OpenStack: