S3

FORKED from astro/s3erl

This is an Erlang client for Amazons Simple Storage Service, aka S3. It is based on the much forked s3erl library, originally written by Andrew Birkett andy@nobugs.org.

This particular version has a few features which we found to be very useful in busier systems where reliability is key.

• Safe retries, your request will suceed or fail within the time you specified, with the user process able to continue execution
• Concurrency is limited to a configurable number of concurrent requests to S3, in which case calls return immediately. This allows the user to decide how to handle overload by for example shedding load, instead of trashing the HTTP client.
• Binaries for keys and values
• Instrumentation, with callbacks after every request, retry or concurrency limit reached.
• Configurable endpoint, which means you can use fakes3 for testing.

Limitations:

• Only one instance of s3_server with one configuration(endpoint, credentials, etc) can exist within the VM as we used named gen_servers.

Usage

Currently, you must add the s3_server to your own supervisor tree, as s3erl does not include it's own supervisor.

s3_spec() ->
    Options =
        [{timeout, 15000},
         {max_concurrency, 500},
         {retry_callback, fun my_module:s3_retry_callback/2},
         {post_request_callback, fun my_module:s3_post_request_callback/3},
         {access_key, "foobar"},
         {secret_access_key, "secret"}],

    {s3, {s3_server, start_link, [Options]},
     permanent, 5000, worker, []}.

You can of course also start s3_server from the shell for experimenting, like this: s3_server:start_link([{access_key, "..."}, {secret_access_key, "..."}])

Then you can start using S3:

1> s3:get("my-bucket", "my-key").
{ok, not_found}
2> s3:put("my-bucket", "my-key", <<"big binary blob">>, "text/plain").
{ok, "etag"}
3> s3:get("my-bucket", "my-key").
{ok, <<"big binary blob">>}

See the test suite in test/s3_test.erl for more examples of usage.

Timeouts

Care has been taken to make sure requests can be retried in a timely and safe manner. If you're doing a significant amount of requests to S3, you will see many requests failing, most of which returns correctly with another attempt.

The behaviour of retries is completely up to the user. s3erl allows you to configure up front how many times you want to retry, the timeout for each request, the delay between requests and a callback function called after every failed request to help you measure and log failed requests.

With the options below, each request from a client process (ie. s3:get/3) is allowed 3 failed requests before it returns with an error. Each request may either return immediately with an error (ie. 500 from S3) or is considered to have timed out after 1000 ms. After each request, there's a think time of 500 ms before retrying the request. The total time s3erl will spend on this request is then 1000 * 3 + 500 * 3 = 4500. When you factor in some slack, a client timeout of 5000 ms in the s3:get/3 is suitable.

[{max_retries, 3},
 {timeout, 1000},
 {retry_delay, 500}]

Running the tests

To run the unit tests, you need to use your own S3 credentials. These should be placed in priv/s3_credentials.term according to the template in priv/s3_credentials.term.template. In priv/bucket.term you can configure which bucket to use. Run the tests with ./rebar skip_deps=true eunit.