Object Store

Chameleon provides an object store service through the OpenStack Swift interface. It is intended to be used for storing and retrieving data used during experiments, such as input files needed for your applications, or results produced by your experiments.

Hint

Chameleon object store service is currently backed by a Ceph cluster with more than 2.1 PB of capacity. The data is replicated, keeping two copies of each object, effectively providing over 1 PB of storage available to users. This storage capacity will increase as the project goes on. The replication should provide good availability in case of hardware failures. However, all copies are kept within the same data center and are not backed up on a separate system; if you feel that this does not provide sufficient reliability in your case, you should consider backing up really critical data externally.

Availability

You can access the Object Store from instances running on CHI@TACC and CHI@UC. Each region has its own store, meaning that objects uploaded to one are not visible to the other. In general you should use the store local to the region where your instances are running for the best performance. To make it easier for you to use the Object Store client, we installed it in all appliances supported by Chameleon. Additionally, you can also access the Object Store from the CHI@TACC or CHI@UC web interfaces under the Object Store panel.

Hint

KVM@TACC users can access the TACC store by using their CHI@TACC OpenStack RC file.

Objects and Containers

Objects are equivalent to individual files. They are stored in Containers, which are data structures that can contain multiple Objects. When uploading Objects, they must be stored inside of Containers. You may perform operations on individual Objects inside Containers, such as downloading or deleting them. You may also work with entire Containers and perform operations such as downloading an entire Container.

Managing Object Store using the GUI

To access the Object Store using the GUI at CHI@TACC or CHI@UC, use the navigation sidebar to go to Project > Object Store > Containers.

Working with Containers

To create a container, click the +Container button. This will open the Create Container dialog.

Choose a unique name of your container and set the visibility to either Public or Not Public. When you are finished, click the Submit button. You will see your new Container appear in the list on the Containers page.

You may click on a Container to see the details and work with Objects belong to it.

Attention

Downloading a container is not available from the GUI. Use the CLI to download containers.

You may delete a container by clicking the Delete icon in the upper right of the Container Detail Panel.

Working with Objects

To upload a local file to a container, click the button with the Upload symbol next to the search bar.

This will open the Upload File dialog.

Choose a file to upload from your local file system and give a name to the object.

Working with Folders

If you wish to create a Folder within your Container, click the +Folder button and give a name to your folder in the Create Folder dialog.

Your new folder will appear in the Container details.

You may browse your folder and upload files to it by clicking on the folder.

Managing Object Store using the CLI

Tip

Reading Command Line Interface (CLI) is highly recommanded before continuing on the following sections.

In addition to Installing the CLI, you must also install python-swiftclient package:

pip install python-swiftclient

Then, you must set environment variables for your account and project using The OpenStack RC Script.

Working with Containers

To create a Container, use the following command:

openstack container create <container_name>

Tip

By default, the Container created using the above command will not be visible to the public.

To view all containers that belong to your project, run:

openstack container list

Tip

You may use --prefix <prefix> as a filter to list the containers whose name starts with <prefix>.

To see details of a container, use the command:

openstack container show <container_name>

To view a list of objects within a container, use the command:

openstack object list <container_name>

To download a container with all the objects belong to it, use the following command:

openstack container save <container_name>

To delete a container and wipe out all the objects belong to it, use the following command, and be careful!

openstack container delete --recursive <container_name>

Working with Objects

You may upload a file from your local machine to a container using the following command:

openstack object create <container_name> <local_filename>

Tip

Optionally, you may name the object differently from it’s original name in your local machine by using the --name parameter.

To delete an object from a container, run:

openstack object delete <container_name> <object_name>

If you wish to download an individual object directly from a container, use the command:

openstack object save <container_name> <object_name>

Large object support

The Swift CLI only supports objects up to 4GB. Larger objects are supported, provided they are uploaded in segments. This advanced functionality is only supported using a separate Swift interface. For a version compatible with Chameleon’s authentication, you need python-swiftclient >= 3.11.1, and to generate and use an Application Credential

pip install "python-swiftclient>=3.11.1"

Instead of invoking commands via openstack, you will instead use the swift command, which supports a --segment-size parameter, specifying the segment size in bits. --segment-size 4831838208 is close to the segment limit of 4GB.

There is also a --changed flag, which prevents uploading of the object if the checksum has not changed:

swift --os-auth-type v3applicationcredential \
--os-application-credential-id <credential_id> \
--os-application-credential-secret <credential_secret> \
upload --changed --segment-size 4831838208 \
<container_name> <path>

Working with Folders

There isn’t “folders” when you managing the Object Store with the CLI. However, when you create an object, you may use the delimiter / to specify the path.

Mounting Object Store as a File System

Tip

rclone can upload small and large files to the object store, however, if you have trouble uploading larger objects, you may need to use the Swift CLI instead.

When logged into an instance using Chameleon-supported images, such as CC-CentOS9-Stream and CC-Ubuntu24.04, you will find a README in the home directory for the cc user. The README describes how to mount containers in the Chameleon Object Store into a directory called cc_my_mounting_point in your home directory. Mounts are facilitated by the rclone tool. If the directory does not exist, this directory will be created the first time you mount a container. Inside the cc_my_mounting_point directory, you will find directories that map to containers you’ve mounted. If there is a directory inside cc_my_mounting_point that is not mounted it should have a file named THIS_IS_NOT_MOUNTED in it. Once you mount the container, the file will no longer be visible until the container is unmounted.

The tool can mount existing containers in the object store, or create them if they don’t exist. The containers are from the specific site where the instance is located and only work at sites that have an object store (currently CHI@UC and CHI@TACC). For example, instances running at CHI@UC will interact with the object store also at CHI@UC. You will not be able to interact with object store data at other sites using this method.

Important

Some older Chameleon-supported images have an outdated mechanism for mounting the object store using cc-cloudfuse. This mechanism for mounting the object store is no longer recommended or supported. On older images you should use the Swift CLI directory to use the object store.

To mount, use the following command:

cc-mount-object-store start your_container_name

Now you can access your Chameleon Object Store as your local file system at: ~/cc_my_mounting_point/your_container_name.

You can investigate if a mount is running for a container with:

cc-mount-object-store status your_container_name

You can also list all running mounts with:

cc-mount-object-store list

To unmount, use the following command:

cc-mount-object-store stop your_container_name

Important

Limitations

The primary usage scenario of the rclone tool is to allow you to interact with Chameleon Object Store using familiar file system operations. Because the tool runs on top of an object store, it is important to understand that not all functionality will behave identically to a regular file system.

Symbolic links, file permissions, and POSIX file locking operations are not supported.
Updating an existing file is an expensive operation as it downloads the entire file to local disk before it can modify the contents.
You can mount from multiple nodes, but there is no synchronization between nodes regarding writes to Object Storage.
The mounting root directory can only contain directories, as they are mapped to Object Store containers.
Renaming directories is not allowed.
It keeps an in-memory cache of the directory structure, so it may not be usable for large file systems. In addition, files added by other applications will not show up until the cache expires.

Please keep these limitations in mind when considering the use of this tool to interact with the object store.

Warning

The use of rclone to sync files between your instance and the object store is a best effort tool. It is the responsibilty of the user to verify the files sync’d correctly and are valid.

Given the challenges of mapping files in a file system to an object store over a network, numerous problems can occur that may impact the availability of files on the object store. If you attempt to copy files into the mount point and receive errors, it is important that you verify the existence and contents of the file in the object store and not simply assume the file has been persisted there (even if it is present in the mount point).