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In continuation to our previous blogs on Components of OpenStack today we are going to learn about next OpenStack Component which is: Image (glance) and we are also going to learn about managing the images in the OpenStack.
So let’s start with Image (Glance):-
The OpenStack Image (Glance) is an image service scheme which offers services like finding, listing, recovering images related to disk and server for users which can upload as well as find data resources which can be used with extra services. It includes images as well as definitions of metadata.
It is a central warehouse for all the images which are virtual. The OpenStack Image (Glance) component uses RESTful API which permits questioning of virtual machine image metadata and also the recovering of real images.
Users can save these Virtual Machine images obtained via Glance in different types of locations such as starting from simple file systems to the OpenStack Swift Project which is an example of object storage systems.
For introducing new instance the images present in the Glance are stored as “Templates”. The Image (Glance) has been designed as a standalone project which is required for organizing huge sets of VM images. It also offers consecutive solutions for the management of cloud disk images. Image (Glance) also takes shots of uninterrupted instances required for taking the backup of virtual machines along with their different states.
As mentioned earlier the Image (Glance) receives API requests for images from the users or from the components of Nova and then stores it in the simple file systems or in the object storage service like Swift or maybe in some other storage warehouse or repository.
Let’s learn about the architecture of Glance: –
As discussed earlier, Image (glance) accepts RESTful API requests for server and it has client-server architecture. The user requests are received via RESTful API and then it waits for authentication from Keystone. The Domain controller of Glance handles all the inner processes that are split into layers and each and every layer applies their own functions. The communication layer between outside storage back ends and the Glance or between the simple file systems is Glance store and it offers consistent interaction for accessing. Every component in the system can access SQL central database which is used by Glance.
As discussed earlier Image (Glance) holds a metadefs catalog which offers the OpenStack community a way for determining various metadata key names programmatically as well as determining the correct values which can be implemented to the resources of OpenStack.
It is important to keep in mind that whatever we are talking here is simply just about a catalog i.e. as mentioned earlier the keys and the values will not perform anything until implemented to every OpenStack resources with the help of the APIs or with the help of the client tools which are offered by the facilities accountable for OpenStack resources.
The relationship between the Image service and the metadefs service is not so special. The Image service API or the client tools are used for applying the keys and values to the images which are defined in the metadefs service and it is similar to the various other OpenStack services.
The roles are assigned to the users by the cloud operator and these roles decide who will upload and handle the images. The cloud operator may limit the uploading and the handling of the images only to the cloud administrators or cloud operators.
The OpenStack image creates command is used for uploading the images or users can also use the Image service API. For managing the image the OpenStack client which offers methods for listing and deleting images, setting and deleting image metadata and for creating images of the constantly streaming requests or shots or the types of backups.
It is important to note that once you upload an image it is not possible to modify it.
We will discuss how to list or get the details for the image, how to create or modify an image, how to create an image with the help of ISO image and how to troubleshoot the creation of an image in our next blog.
That’s all for today! I hope you find this information helpful. If you have any questions regarding today’s article you can comment it in the comment section below. See you soon with another interesting article.
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