Public buckets

You can use the S3 API to configure a bucket with public read access, so that anyone can download its objects with a web browser. Making a bucket globally readable entails setting a bucket policy that enables read access on all its objects.

Setting a bucket policy affects all objects in a bucket. To avoid inadvertent disclosure of existing information, consider setting public read policies only on empty buckets.

Prerequisites

Object versioning requires that you configure your environment with working S3-compatible credentials.

Setting a public read policy for a bucket

First, create a local policy file named policy.json, with the following content (replace <bucket-name> with the name of your bucket):

{ 
  "Statement": [ 
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::<bucket-name>/*"
    }
  ]
}

To apply this policy to a bucket such that read-only access is permitted for everyone, run the following command:

awsmcs3cmd

aws --profile <region> \
  s3api put-bucket-policy \
  --policy file://policy.json \
  --bucket <bucket-name>

mc anonymous set-json policy.json <region>/<bucket-name>

s3cmd -c ~/.s3cfg-<region> setpolicy policy.json s3://<bucket-name>

Accessing objects in a public bucket

To access an object in a public bucket from a web browser or a generic HTTP/HTTPS client like curl, you must construct its URI as follows:

https://s3-<region>.citycloud.com/<project-uuid>:<bucket-name>/object-name

Your project UUID is listed as the project_id field in the output of the openstack ec2 credentials create command you used to create your S3-compatible credentials.

If you did not note it down at the time of account creation, you can always retrieve it with openstack ec2 credentials <access-key>.

For example, to retrieve an object named bar.pdf in a bucket named foo from the project with the UUID 07576783684248f7b2745e34356c6025 in the Cleura Cloud Kna1 region, you would run:

$ curl -O https://s3-kna1.citycloud.com/07576783684248f7b2745e34356c6025:foo/bar.pdf
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 62703  100 62703    0     0   186k      0 --:--:-- --:--:-- --:--:--  186k

Public bucket accessibility via the Swift API

Once you make a bucket public via the S3 API, its objects also become accessible via the corresponding Swift API path.

Thus, the following URL paths allow you to retrieve the same public object:

• https://s3-kna1.citycloud.com/07576783684248f7b2745e34356c6025:foo/bar.pdf
• https://swift-kna1.citycloud.com/swift/v1/AUTH_07576783684248f7b2745e34356c6025/foo/bar.pdf

Enabling bucket listing

The policy.json file above allows anyone to retrieve known objects by name, but does not enable listing the bucket’s contents. Most of the time, this is what you want.

However, in case you do need unauthenticated clients to be able to list all objects in a bucket, modify your policy.json file as in the following example:

{
  "Statement": [ 
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::<bucket-name>/*"
    },
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:ListBucket",
      "Resource": "arn:aws:s3:::<bucket-name>"
    }
  ]
}

Note that for the s3:GetObject action, /* follows the bucket name, whereas for the s3:ListBucket action you specify just the bucket name with no suffix.

Once you have updated your local policy.json file, apply it just as when you created the policy.

You can then open a bucket path in your browser, to retrieve an XML document containing a list of all objects in the bucket. You would construct the URL by the following schema:

https://s3-<region>.citycloud.com/<project-uuid>:<bucket-name>

Removing a public read policy from a bucket

If you want to remove a previously-set public read policy from a bucket, and revert to its default policy that requires authentication on every object access, run the following command:

awsmcs3cmd

aws --profile <region> \
  s3api delete-bucket-policy \
  --bucket <bucket-name>

mc anonymous set none <region>/<bucket-name>

s3cmd -c ~/.s3cfg-<region> delpolicy s3://<bucket-name>