Openstack Swift

OpenStack Swift -- Object Storage Service

Swift provides distributed object storage with an HTTP-accessible API. Unlike block storage (Cinder), which provides attached devices, Swift stores objects (files) in containers (buckets) accessible via REST API calls. Swift is S3-compatible when the s3api middleware is enabled, making it a drop-in replacement for AWS S3 in many applications.

Architecture

Swift uses a ring architecture to determine where objects are stored. Even in a single-node deployment, understanding rings is important because they control data placement and replication.

• Rings: Swift maintains three rings -- account, container, and object. Each ring maps a partition to a set of devices (disks). The ring builder calculates this mapping based on the number of replicas, partition power, and device weights.
• Partition power: Determines how many partitions exist (2^power). Higher partition power = more granular distribution but more memory usage. Single-node typically uses partition power 10 (1024 partitions).
• Replicas: The number of copies of each object. Production uses 3 replicas across failure zones. Single-node uses 1 replica (no redundancy benefit with one node).
• Eventual consistency: Swift is designed around eventual consistency. After a write, reads from different nodes may temporarily return different results. Replicator and auditor processes converge state over time.

Service components:

• swift-proxy: The API frontend. Receives HTTP requests, authenticates via Keystone, routes requests to the appropriate storage nodes using the rings.
• swift-account: Manages account-level metadata and container listings.
• swift-container: Manages container-level metadata and object listings.
• swift-object: Stores and retrieves actual object data on disk.
• Auxiliary services: object-replicator, object-auditor, container-updater, account-reaper (background consistency processes).

Deploy

Kolla-Ansible Configuration

Key settings in globals.yml:

# Enable Swift
enable_swift: "yes"

# Disk configuration for Swift storage
# Kolla-Ansible expects dedicated disks or partitions
# Format: label:device pairs
swift_devices_name: "KOLLA_SWIFT_DATA"

# Number of replicas (1 for single-node)
swift_default_replication_count: 1

Disk Setup for Swift

Swift requires dedicated storage devices. For Kolla-Ansible:

# Format and label a disk for Swift
parted /dev/sdc mklabel gpt
parted /dev/sdc mkpart primary xfs 0% 100%
mkfs.xfs -f /dev/sdc1
# Label must match swift_devices_name
xfs_admin -L KOLLA_SWIFT_DATA /dev/sdc1

# Alternatively, use a loop device for testing
dd if=/dev/zero of=/srv/swift-disk bs=1M count=10240
mkfs.xfs -f /srv/swift-disk
# Mount and label for Kolla-Ansible discovery

Ring Building (Single-Node)

Kolla-Ansible builds rings during deployment. For single-node with 1 replica:

# Kolla-Ansible handles ring building, but for manual ring management:
# Account ring
swift-ring-builder account.builder create 10 1 1
swift-ring-builder account.builder add --region 1 --zone 1 \
  --ip 10.0.0.1 --port 6202 --device sdc1 --weight 100
swift-ring-builder account.builder rebalance

# Container ring (same pattern)
swift-ring-builder container.builder create 10 1 1
swift-ring-builder container.builder add --region 1 --zone 1 \
  --ip 10.0.0.1 --port 6201 --device sdc1 --weight 100
swift-ring-builder container.builder rebalance

# Object ring (same pattern)
swift-ring-builder object.builder create 10 1 1
swift-ring-builder object.builder add --region 1 --zone 1 \
  --ip 10.0.0.1 --port 6200 --device sdc1 --weight 100
swift-ring-builder object.builder rebalance

Container and Service Verification

# List Swift containers
docker ps --format '{{.Names}}' | grep swift

# Expected containers:
# swift_proxy_server, swift_account_server, swift_container_server,
# swift_object_server, swift_account_reaper, swift_object_expirer,
# swift_rsyncd

# Verify Swift is operational
openstack object store account show
# Should return account info with container count and bytes used

# Check S3 API availability (if s3api middleware is enabled)
# Use AWS CLI or s3cmd with OpenStack credentials

Configure

Storage Policies

Storage policies define different tiers of storage with different replication counts, erasure coding parameters, or device assignments.

# In swift.conf (through Kolla-Ansible config override)
[storage-policy:0]
name = standard
default = yes

# Additional policies for different tiers:
# [storage-policy:1]
# name = high-durability
# (requires separate ring and additional devices)

S3 API Middleware

Swift's s3api middleware provides S3-compatible API access:

# In proxy-server.conf pipeline (Kolla-Ansible configures this when enabled)
# pipeline = ... s3api s3token keystoneauth ... proxy-server

Using the S3 API:

# Create EC2 credentials for S3 access
openstack ec2 credentials create

# Use with AWS CLI
aws configure
# AWS Access Key ID: <ec2-access>
# AWS Secret Access Key: <ec2-secret>
# Default region: RegionOne

# Use with endpoint URL
aws --endpoint-url http://<swift-proxy>:8080 s3 ls
aws --endpoint-url http://<swift-proxy>:8080 s3 mb s3://my-bucket
aws --endpoint-url http://<swift-proxy>:8080 s3 cp file.txt s3://my-bucket/

Container ACLs

Swift provides container-level and account-level access control:

# Make a container publicly readable
swift post my-container --read-acl ".r:*,.rlistings"

# Grant read access to a specific project
swift post my-container --read-acl "<project-id>:*"

# Grant write access to a specific user
swift post my-container --write-acl "<project-id>:<user-id>"

# Remove ACLs
swift post my-container --read-acl "" --write-acl ""

TempURL Configuration

TempURL allows generating time-limited URLs for unauthenticated access:

# Set the tempurl key on the account
swift post -m "Temp-URL-Key: mysecretkey"

# Generate a tempurl (valid for 3600 seconds)
swift tempurl GET 3600 /v1/AUTH_<account>/my-container/my-object mysecretkey

Large Object Support

Swift has a 5GB limit per single object. For larger files, use segmented uploads:

• SLO (Static Large Object): Upload segments, then create a manifest listing all segments. Immutable after creation.
• DLO (Dynamic Large Object): Upload segments with a common prefix. The manifest points to the prefix. Segments can be modified independently.

# SLO upload using swift CLI
swift upload my-container --segment-size 1073741824 large-file.iso
# Creates segments in my-container_segments/ and a manifest in my-container/

# DLO: manually upload segments with shared prefix
swift upload my-container_segments segment-001 segment-002 segment-003
swift upload my-container large-file --header "X-Object-Manifest: my-container_segments/segment-"

Object Versioning

# Enable versioning on a container
swift post my-container -H "X-Versions-Location: my-container-versions"
# Create the versions container
swift post my-container-versions

# Now every overwrite of an object in my-container stores the
# previous version in my-container-versions

Object Expiry

# Set an object to expire after 86400 seconds (24 hours)
swift post my-container my-object -H "X-Delete-After: 86400"

# Set an object to expire at a specific Unix timestamp
swift post my-container my-object -H "X-Delete-At: 1771900000"

Rate Limiting

# In proxy-server.conf (through config override)
[filter:ratelimit]
account_ratelimit = 100    # requests per second per account
container_ratelimit_0 = 50  # requests per second for containers with 0+ objects

Operate

Container and Object CRUD

# Create a container
openstack container create my-container

# Upload an object
openstack object create my-container local-file.txt

# List containers and objects
openstack container list
openstack object list my-container

# Download an object
openstack object save my-container remote-file.txt --file local-copy.txt

# Delete an object and container
openstack object delete my-container remote-file.txt
openstack container delete my-container

Using the Swift CLI

The swift CLI provides additional functionality beyond the OpenStack unified CLI:

# Upload with metadata
swift upload my-container file.txt --header "X-Object-Meta-Author: admin"

# Show container metadata
swift stat my-container

# Show object metadata
swift stat my-container file.txt

# Bulk delete
swift delete my-container --prefix "logs/"

Storage Usage Reporting

# Account-level usage
openstack object store account show
# Shows: Account, Containers, Objects, Bytes, Content-Type

# Per-container usage
swift stat my-container
# Shows: Object Count, Bytes Used, Read/Write ACLs

Ring Rebalancing

When adding or removing devices (relevant for future multi-node expansion):

# Add a new device to the object ring
swift-ring-builder object.builder add --region 1 --zone 2 \
  --ip 10.0.0.2 --port 6200 --device sdb1 --weight 100

# Rebalance (distributes partitions to new devices)
swift-ring-builder object.builder rebalance

# Distribute updated ring files to all nodes
# Kolla-Ansible: kolla-ansible -i inventory reconfigure -t swift

Troubleshoot

Object Upload Failures

Symptoms: PUT requests return 503 Service Unavailable or timeout; swift upload hangs.

Diagnostic sequence:

1. Check storage space: df -h on Swift storage devices. If devices are full (>90%), Swift returns 503.
2. Check ring configuration: swift-ring-builder object.builder to verify devices are listed with appropriate weight. Missing devices prevent uploads.
3. Check proxy logs: docker logs swift_proxy_server 2>&1 | tail -50. Look for connection refused errors to object servers.
4. Check object server: docker logs swift_object_server 2>&1 | tail -50. Look for disk I/O errors or permission issues.
5. Check XFS filesystem: xfs_repair -n /dev/sdc1. XFS corruption can cause silent write failures. Note: xfs_repair requires the filesystem to be unmounted.

S3 API Compatibility Issues

Symptoms: AWS CLI or S3 clients return authentication errors, "unsupported operation," or unexpected response format.

Diagnostic sequence:

1. Check middleware pipeline: Verify s3api and s3token are in the proxy-server pipeline. docker exec swift_proxy_server grep pipeline /etc/swift/proxy-server.conf.
2. Check EC2 credentials: openstack ec2 credentials list. Credentials must exist for the user.
3. Signature version: Swift s3api supports both V2 and V4 signatures. If using V4, ensure the region is correct. Some older clients default to V2.
4. Unsupported operations: Swift's S3 API does not support all S3 features (e.g., bucket policies, object lock, some multipart upload options). Check the Swift s3api compatibility matrix.
5. Check endpoint URL: The S3 endpoint is typically on port 8080 (same as Swift API), not 443. Ensure the client is configured with the correct endpoint.

Container Listing Empty or Incomplete

Symptoms: Container exists and objects were uploaded, but listing returns empty or partial results.

Diagnostic sequence:

1. Eventual consistency: Swift container listings are eventually consistent. After a burst of uploads, the container server may not have processed all updates yet. Wait 30-60 seconds and retry.
2. Container server health: docker logs swift_container_server 2>&1 | tail -50. If the container server is overloaded or has disk issues, updates may be delayed.
3. Container updater: docker logs swift_container_updater 2>&1 | tail -20. The updater processes deferred container updates. Check for errors.
4. Object count vs listing: swift stat my-container shows the stored object count. If the count is correct but listing is wrong, the container database may need repair.

Permission Denied on Container Operations

Symptoms: 403 Forbidden when creating containers, uploading objects, or reading container contents.

Diagnostic sequence:

1. Check ACLs: swift stat my-container -- look at Read ACL and Write ACL fields. Verify the user/project has appropriate access.
2. Check Keystone role: openstack role assignment list --user <user> --project <project>. User needs at least member role (or swiftoperator if configured).
3. Check account ownership: The Swift account maps to a Keystone project. Verify the user is a member of the correct project.
4. Check reseller prefix: Swift uses AUTH_ prefix by default for Keystone integration. Ensure the account name matches AUTH_<project-id>.
5. Check proxy auth pipeline: docker exec swift_proxy_server grep -A5 keystoneauth /etc/swift/proxy-server.conf. Verify operator_roles includes the user's role.

Ring Builder Errors

Symptoms: Ring rebalance fails, or Swift cannot find devices.

Diagnostic sequence:

1. No devices added: swift-ring-builder <ring>.builder -- if no devices are listed, none were added to the ring. Add devices before rebalancing.
2. Partition power mismatch: All three rings (account, container, object) must use the same partition power. Mismatched rings cause routing failures.
3. Minimum partition hours: Ring builder enforces a minimum time between rebalances. If rebalancing too frequently, wait for the cooldown period.
4. Weight zero: Devices with weight 0 are being drained. Ensure at least one device has positive weight.
5. Ring file distribution: After rebalancing, ring files (.ring.gz) must be distributed to all Swift nodes. On single-node, this happens automatically. Multi-node requires manual or Kolla-Ansible reconfigure.

Integration Points

• Keystone: All Swift API calls authenticate through Keystone. Swift uses Keystone tokens for native API access and EC2 credentials for S3 API access. The keystoneauth middleware in the proxy pipeline maps Keystone roles to Swift ACL concepts. Swift accounts map to Keystone projects via the AUTH_<project-id> naming convention.
• Glance: Swift can serve as a backend store for Glance images. When configured, Glance stores image data as objects in Swift containers, providing object-level durability for image files.
• Cinder: Cinder's backup service can use Swift as a backup target (cinder_backup_driver: swift). Volume backups are stored as segmented objects in Swift containers.
• TempURL: Provides time-limited unauthenticated access to objects. Useful for sharing files with external users or applications that cannot perform Keystone authentication. Requires the tempurl middleware in the proxy pipeline.

NASA SE Cross-References