TransferManager hitting "Connection Reset"

[rcoh]

We're using the transfer manager to download files but periodically running into the following (full stack trace at bottom)

com.amazonaws.AmazonClientException: Unable to store object contents to disk: Connection reset

The documentation seems to indicate that this happens when a connection is reused too many times:

Also, don't overuse a connection. Amazon S3 will accept up to 100 requests before it closes a connection (resulting in 'connection reset'). Rather than having this happen, use a connection for 80-90 requests before closing and re-opening a new connection.

Obviously we can retry these requests, but it isn't ideal. Is it something we're doing wrong with the library that's causing this? Or is the library not managing connections properly?

com.amazonaws.AmazonClientException: Unable to store object contents to disk: Connection reset
    at com.amazonaws.services.s3.internal.ServiceUtils.downloadObjectToFile(ServiceUtils.java:270)
    at com.amazonaws.services.s3.internal.ServiceUtils.retryableDownloadS3ObjectToFile(ServiceUtils.java:344)
    at com.amazonaws.services.s3.transfer.TransferManager$2.call(TransferManager.java:731)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:196)
    at java.net.SocketInputStream.read(SocketInputStream.java:122)
    at sun.security.ssl.InputRecord.readFully(InputRecord.java:442)
    at sun.security.ssl.InputRecord.readV3Record(InputRecord.java:554)
    at sun.security.ssl.InputRecord.read(InputRecord.java:509)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:934)
    at sun.security.ssl.SSLSocketImpl.readDataRecord(SSLSocketImpl.java:891)
    at sun.security.ssl.AppInputStream.read(AppInputStream.java:102)
    at org.apache.http.impl.io.AbstractSessionInputBuffer.read(AbstractSessionInputBuffer.java:198)
    at org.apache.http.impl.io.ContentLengthInputStream.read(ContentLengthInputStream.java:178)
    at org.apache.http.conn.EofSensorInputStream.read(EofSensorInputStream.java:137)
    at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:71)
    at com.amazonaws.event.ProgressInputStream.read(ProgressInputStream.java:151)
    at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:71)
    at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:71)
    at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:71)
    at com.amazonaws.event.ProgressInputStream.read(ProgressInputStream.java:151)
    at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:71)
    at java.io.FilterInputStream.read(FilterInputStream.java:107)
    at com.amazonaws.services.s3.internal.ServiceUtils.downloadObjectToFile(ServiceUtils.java:265)
    ... 6 more

[david-at-aws]

According to that stack trace you've made it to the point where you're reading the object content, which means S3 sent you a successful response; the connection is not getting reset because we've accidentally exceeded the service's 100-requests-per-connection limit. Something else is going wrong that's resetting the connection mid-download. Unfortunately it's hard to say what - connections can be reset by anyone on the network between you and S3 for many different reasons. :(

If you can grab request ids for some of these failed requests (maybe by turning on Apache HttpClient header logging?), the S3 team can double-check what's happening on their end for these requests. If you can grab a packet capture from your end that would also be interesting (although it'll presumably be quite large if you're pulling a bunch of data from S3).

If you can't uncover the root cause of the resets, retries are your only recourse. The TransferManager has retries built in, but it's explicitly not retrying on SocketException. Strange... I'll chase down whether it's safe for us to add retries on SocketException in a future release - from a quick glance it seems like we should be able to.

[rcoh]

Thanks. Unfortunately given our data volumes and the rarity of this exception we can't feasibly do that amount of logging. Retrying should work fine though. Thanks!

[acmcelwee]

I'm seeing this pretty consistently, as well. I'm using the transferManager.downloadDirectory to download directories with a mix of file sizes, from a few kilobytes to a few gigabytes. The total directory sizes range from 40-80G. For now, I've wrapped my downloadDirectory calls in retry logic, but from reading the downloadDirectory code, retrying at that level means that you lose any progress you've made so far, since it passes false for resumeExistingDownload. Retrying within the transferManager layer seems like it would help a lot by executing the retries at the s3 object level, retaining the progress that's been made in downloading the overall directory, so far. Either handling retries of SocketException, or allowing resumable calls of downloadDirectory would be enough to resolve the issue for me.

AWS SDK Version: 1.9.39

EDIT:
I'll also mention that I've tried tweaking the following settings in the ClientConnection of my s3 client passed to the transfer manager:

• raising/lowering socket and connection timeouts
• lowering the connection ttl
• raise/lower the max connections
  I think the one that's helped the most was lowering the connection ttl, but the issue still persists. I'll also note that for all cases, I'm using the transfer manager within a host on ec2.

[david-at-aws]

Adding an option to do resumable downloadDirectory calls sounds like a good idea. I'll add that to our backlog, or would be happy to take a look at a pull request if you'd like to put one together. I'd also still very much like to figure out a way to retry on SocketExceptions without causing trouble for aborts, but haven't had a chance to dig into it yet.

[acmcelwee]

@david-at-aws PR here. However, I looked for the test suite for the s3 and TransferManager stuff, but I'm not finding anything. Is there a suite that I can validate my PR against and update w/ a test for the resume functionality? What's the common contributor workflow for people validating their changes w/ their own projects? Publish an artifact to either local or my own nexus repo?

[david-at-aws]

We've got a test suite internally that we run changes through before merging them. We realize it'd be much better for you to be able to run the tests yourself before sending us the PR, and we're working on separating it from some Amazon-internal infrastructure it currently depends on so we can publish it on GitHub - unfortunately not quite there yet.

[acmcelwee]

Got it. Do you publish nightly snapshots that I could pull into a project?

Also, an update on the original issue: Enabling tcp keepalive in the ClientConnection and lowering my connection ttl seems to be the most effective thing I've found at reducing the frequency of the "Connection Reset" exception.

[l15k4]

Shouldn't the RetryPolicy make a new request when this happens? So that the exception doesn't bubble up and the file is downloaded again if it failed before?

[l15k4]

I'm using version 1.10.26 and when I download in parallel by 3 threads (each having its ownclient instance) I'm getting following error very frequently :

Caused by: java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:209) ~[na:1.8.0_45]
at java.net.SocketInputStream.read(SocketInputStream.java:141) ~[na:1.8.0_45]
at org.apache.http.impl.io.AbstractSessionInputBuffer.read(AbstractSessionInputBuffer.java:198) ~[gwiq.jar:0.9-SNAPSHOT]
at org.apache.http.impl.io.ContentLengthInputStream.read(ContentLengthInputStream.java:178) ~[gwiq.jar:0.9-SNAPSHOT]
at org.apache.http.conn.EofSensorInputStream.read(EofSensorInputStream.java:137) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:72) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.event.ProgressInputStream.read(ProgressInputStream.java:151) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:72) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:72) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:72) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.event.ProgressInputStream.read(ProgressInputStream.java:151) ~[gwiq.jar:0.9-SNAPSHOT]
at java.security.DigestInputStream.read(DigestInputStream.java:161) ~[na:1.8.0_45]
at com.amazonaws.services.s3.internal.DigestValidationInputStream.read(DigestValidationInputStream.java:59) ~[gwiq.jar:0.9-SNAPSHOT]
at com.amazonaws.internal.SdkFilterInputStream.read(SdkFilterInputStream.java:72) ~[gwiq.jar:0.9-SNAPSHOT]
at java.io.BufferedInputStream.fill(BufferedInputStream.java:246) ~[na:1.8.0_45]
at java.io.BufferedInputStream.read1(BufferedInputStream.java:286) ~[na:1.8.0_45]
at java.io.BufferedInputStream.read(BufferedInputStream.java:345) ~[na:1.8.0_45]
at java.io.FilterInputStream.read(FilterInputStream.java:107) ~[na:1.8.0_45]

[l15k4]

I noticed that this happens in "lazy" environment when the stream isn't read right after the connection returns the response. For instance if you create an Iterator of s3Obj and read its content lazily while iterating it...

[jtrunick]

I'm running into this issue as well. Any suggestions as to ideal configuration parameters appreciated. @acmcelwee