Object store configuration

cnmsql uses an S3-compatible object store for physical backups and continuous binlog archiving. The same S3ObjectStore API is used by one-shot Backups, ScheduledBackup-generated Backups, recovery, and PITR.

Minimal MinIO-style configuration

spec:
  backup:
    objectStore:
      bucket: cnmsql-backups
      path: production
      endpoint: http://minio.minio.svc:9000
      region: us-east-1
      forcePathStyle: true
      credentials:
        accessKeyId:
          name: minio-creds
          key: accessKey
        secretAccessKey:
          name: minio-creds
          key: secretKey

forcePathStyle: true is the compatibility-friendly default and is required by many S3-compatible providers such as MinIO and Ceph RGW.

AWS-style configuration

spec:
  backup:
    objectStore:
      bucket: cnmsql-prod-backups
      path: clusters
      region: eu-west-1
      forcePathStyle: false
      credentials:
        inheritFromIAMRole: true

When endpoint is empty, cnmsql targets AWS S3. With no static credentials configured, workers fall back to the ambient AWS credential chain, in order: the AWS_* environment variables, the shared credentials file, and then the instance metadata endpoint. That last step covers both an EC2 instance profile and an IRSA web-identity token projected into the pod.

Per-backup override

A Backup can override the Cluster object store:

apiVersion: mysql.cnmsql.co/v1alpha1
kind: Backup
metadata:
  name: backup-to-dr-bucket
spec:
  cluster:
    name: cluster-sample
  objectStore:
    bucket: cnmsql-dr-backups
    path: manual
    endpoint: https://s3.example.com
    credentials:
      accessKeyId:
        name: dr-s3-creds
        key: accessKey
      secretAccessKey:
        name: dr-s3-creds
        key: secretKey

If omitted, the Backup uses Cluster.spec.backup.objectStore.

An objectStore also attaches to an externalClusters entry, which enables raw object-store recovery: a new Cluster bootstraps from the bucket directly, without a Backup CR.

Fields

Field	Purpose
bucket	Destination bucket. Required.
path	Key prefix inside the bucket. Optional.
endpoint	S3-compatible endpoint. Empty means AWS S3.
region	Signing and regional endpoint region. When empty, cnmsql signs with auto against Cloudflare R2 and us-east-1 elsewhere.
forcePathStyle	Path-style addressing for MinIO/Ceph-style stores.
signatureVersion	s3v4 by default, s3v2 for legacy providers.
serverSideEncryption	SSE header on every upload: AES256, aws:kms, or aws:kms:<key-id>. Leave unset outside AWS.
storageClass	Storage class of every upload, e.g. STANDARD_IA. Leave unset on providers with a single class.
credentials	Static Secret references or IAM inheritance.
tls	Endpoint TLS verification settings.

TLS settings

Use a custom CA bundle for private endpoints:

tls:
  caBundleSecret:
    name: objectstore-ca
    key: ca.crt

For local testing only:

tls:
  insecureSkipVerify: true

Do not use insecure TLS settings in production.

Object layout

Physical backups:

<path>/<cluster>/<backup-name>/<backup-id>/backup.xbstream
<path>/<cluster>/<backup-name>/<backup-id>/metadata.json

Continuous binlog archive:

<path>/<cluster>/binlogs/<server-uuid>/<binlog-file>
<path>/<cluster>/binlogs/<server-uuid>/<binlog-file>.json
<path>/<cluster>/binlogs/<server-uuid>/_archive_status.json
<path>/<cluster>/binlogs/_index.json

The path value should be unique per environment. cnmsql checks for existing cluster archive prefixes in some recovery/archive paths to avoid adopting an unrelated destination.

Credential placement

One-shot backup Jobs receive object-store credentials only for the duration of the Job.

Recovery init containers receive read access so they can download base backups and binlogs.

Continuous archiving writes from the primary instance manager, so instance Pods need object-store write credentials when archiving is enabled.

Integrity

cnmsql records SHA256 checksums in metadata. S3 ETag is not treated as the integrity source of truth because multipart uploads and provider behavior make ETag semantics inconsistent.

Recovery verifies checksums before trusting downloaded backup data.

S3 compatibility

cnmsql restricts itself to the part of the S3 API that compatible stores implement consistently. The whole of it is PutObject (including multipart uploads of unknown length, which is how a streamed base backup is written), GetObject, HeadObject, ListObjectsV2 (with a fallback to the original listing API, see below), and DeleteObject on a single key.

The operations providers most often omit or restrict are not used at all:

• No bulk delete. Expiring a base backup deletes its objects one request at a time rather than through the POST ?delete multi-object API. Retention is slower on a large archive, but it works everywhere.
• No prefix delete. No provider offers one, so "delete this backup directory" is always a list followed by per-object deletes.
• No bucket lifecycle, versioning, tagging or ACL calls. cnmsql drives retention itself, so a bucket with no lifecycle policy configured behaves exactly as documented here.
• No ETag-based integrity. ETag semantics differ across providers for multipart objects, so cnmsql verifies against SHA256 checksums it records in its own metadata.

Where a missing object is a legitimate outcome, it is reported as a miss rather than an error. That covers a retention pass re-running after an interruption and a probe for an archive that does not exist yet. Providers differ in how they spell a 404, so cnmsql keys off the HTTP status rather than the error code string.

Listing API fallback

Modern stores speak ListObjectsV2, but a few endpoints implement only the original listing API and reject V2 with a 400. The Google Cloud Storage XML interop API is the one you are most likely to meet. cnmsql detects the rejection and falls back to V1 listing for the rest of the process's life. You do not need to configure anything.

Provider matrix

Provider	Status	Notes
MinIO	Verified	forcePathStyle: true. Region defaults to us-east-1. Exercised by the e2e suite on every CI run.
SeaweedFS	Verified	forcePathStyle: true. Requires an s3.config identity with Admin/Read/Write/List.
AWS S3	Expected to work	Leave endpoint empty, set the real region, prefer credentials.inheritFromIAMRole with IRSA. The only provider where serverSideEncryption and storageClass are broadly meaningful.
Ceph RGW	Expected to work	forcePathStyle: true.
Cloudflare R2	Expected to work	Leave region empty (cnmsql signs with auto, which is the only region R2 accepts). Do not set serverSideEncryption: R2 encrypts at rest unconditionally and rejects the header.
Backblaze B2	Expected to work	Use the S3-compatible endpoint for your bucket's region. Do not set storageClass.
GCS (XML interop)	Expected to work	Uses the V1 listing fallback described above. Requires HMAC interoperability keys, not a service-account JSON.

"Verified" means the conformance suite below passes against it. The rest match each provider's documented API surface but nobody has run the suite against them. If you do, the output says exactly which operations failed, and we would like to hear about it.

Qualifying a provider

Before trusting a store with your backups, run the object-store conformance suite against it. It performs the same operations cnmsql's backup, archiving, recovery and retention paths perform. Everything it writes goes under a unique prefix that it removes on the way out, so it is safe to point at a real (empty) bucket:

export cnmsql_S3_ENDPOINT=https://s3.example.com
export cnmsql_S3_BUCKET=cnmsql-conformance
export cnmsql_S3_ACCESS_KEY_ID=... cnmsql_S3_SECRET_ACCESS_KEY=...
export cnmsql_S3_FORCE_PATH_STYLE=true   # omit for AWS S3

make test-s3-conformance

Each operation is a separate subtest, so a provider that fails one tells you precisely which cnmsql feature it cannot support:

--- PASS: TestConformance/Upload_of_unknown_length_(multipart)
--- PASS: TestConformance/Remove_is_idempotent
--- FAIL: TestConformance/RemovePrefix_empties_the_prefix

A failure in RemovePrefix or Remove_is_idempotent means retention will not be able to expire backups on that provider. A failure in the multipart upload means base backups cannot be written at all.

Two settings exist for stores that predate the current API: set signatureVersion: s3v2 only when the provider cannot do v4 signing, and point tls.caBundleSecret at a PEM when the endpoint is fronted by a private CA.