How to make 10,000 files in S3 public

You can generate a bucket policy (see example below) which gives access to all the files in the bucket. The bucket policy can be added to a bucket through AWS console.

{
    "Id": "...",
    "Statement": [ {
        "Sid": "...",
        "Action": [
            "s3:GetObject"
        ],
        "Effect": "Allow",
        "Resource": "arn:aws:s3:::bucket/*",
        "Principal": {
            "AWS": [ "*" ]
        }
    } ]
}

Also look at following policy generator tool provided by Amazon.

http://awspolicygen.s3.amazonaws.com/policygen.html

If you are uploading for the first time, you can set the files to be public on upload on the command line:

aws s3 sync . s3://my-bucket/path --acl public-read

As documented in Using High-Level s3 Commands with the AWS Command Line Interface

Unfortunately it only applies the ACL when the files are uploaded. It does not (in my testing) apply the ACL to already uploaded files.

If you do want to update existing objects, you used to be able to sync the bucket to itself, but this seems to have stopped working.

[Not working anymore] This can be done from the command line:

aws s3 sync s3://my-bucket/path s3://my-bucket/path --acl public-read

(So this no longer answers the question, but leaving answer for reference as it used to work.)

I had to change several hundred thousand objects. I fired up an EC2 instance to run this, which makes it all go faster. You'll want to install the aws-sdk gem first.

Here's the code:

require 'rubygems'
require 'aws-sdk'


# Change this stuff.
AWS.config({
    :access_key_id => 'YOURS_HERE',
    :secret_access_key => 'YOURS_HERE',
})
bucket_name = 'YOUR_BUCKET_NAME'


s3 = AWS::S3.new()
bucket = s3.buckets[bucket_name]
bucket.objects.each do |object|
    puts object.key
    object.acl = :public_read
end

I had the same problem, solution by @DanielVonFange is outdated, as new version of SDK is out.

Adding code snippet that works for me right now with AWS Ruby SDK:

require 'aws-sdk'

Aws.config.update({
  region: 'REGION_CODE_HERE',
  credentials: Aws::Credentials.new(
    'ACCESS_KEY_ID_HERE',
    'SECRET_ACCESS_KEY_HERE'
  )
})
bucket_name = 'BUCKET_NAME_HERE'

s3 = Aws::S3::Resource.new
s3.bucket(bucket_name).objects.each do |object|
  puts object.key
  object.acl.put({ acl: 'public-read' })
end

Just wanted to add that with the new S3 Console you can select your folder(s) and select Make public to make all files inside the folders public. It works as a background task so it should handle any number of files.