Not able to configure Elasticsearch snapshot repository using OCI Amazon S3 Compatibility API

I hope you are aware of when to use S3 Compatible API.

"endpoint":"OCI_TENANCY.compat.objectstorage.OCI_REGION.oraclecloud.com"

Please modify OCI_TENANCY to TENANCY_NAMESPACE. Please refer to this link for more information.

You can find your tenancy namespace information in Administration -> Tenancy Details page.

Well you shouldn't be talking to es-backup.OCI_TENANCY.compat.objectstorage.OCI_REGION.oraclecloud.com where your bucket name is part of the domain. You can try it in your browser and you'll get a similar security warning about certs.

If you look at https://docs.cloud.oracle.com/en-us/iaas/Content/Object/Tasks/s3compatibleapi.htm#usingAPI you'll see a mention of:

The application must use path -based access. Virtual host-style access (accessing a bucket as bucketname.namespace.compat.objectstorage.region.oraclecloud.com) is not supported.

AWS is migrating from path based to sub-domain based URLs for S3 (https://aws.amazon.com/blogs/aws/amazon-s3-path-deprecation-plan-the-rest-of-the-story/) so the ES S3 plugin is probably defaulting to doing things the new AWS way.

Does it make a difference if you use an https:// URL for the endpoint value? Looking at my 6.8 config I have something like:

{  "s3-repository": {    "type": "s3",    "settings": {      "bucket": "es-backup",      "client": "default",      "endpoint": "https://{namespace}.compat.objectstorage.us-ashburn-1.oraclecloud.com/",      "region": "us-ashburn-1"    }  }}

What I'm guessing is that having a full URL for the endpoint probably sets the protocol and path_style_access or 6.8 didn't require you to set path_style_access to true but 7.8 might. Either way, try a full URL or setting path_style_access to true. Relevant docs at https://www.elastic.co/guide/en/elasticsearch/plugins/master/repository-s3-client.html