Stop retrying if we find a permanent url error. (#85)

* Detecting if the transport error was not temporary in which case we stop retrying. Changed bug where get results was being called before we checked for an error.

* Adding exception for EOF error. All EOF errors will be retried.

* Addressing race conditions that may happen when client is closed or connection is re-established.

* Adding documentation about how this particular implemantion of the realis client uses retries in scenarios where a temporary error is found.

realis.go

@@ -251,6 +251,10 @@ func newTBinTransport(url string, timeout int, config *RealisConfig) (thrift.TTr
 	return trans, err
 }
 
+// This client implementation of the realis interface uses a retry mechanism for all Thrift Calls.
+// It will retry all calls which result in a temporary failure as well as calls that fail due to an EOF
+// being returned by the http client. Most permanent failures are now being caught by the thriftCallWithRetries
+// function and not being retried but there may be corner cases not yet handled.
 func NewRealisClient(options ...ClientOption) (Realis, error) {
 	config := &RealisConfig{}
 
@@ -443,7 +447,7 @@ func newTJSONConfig(url string, timeoutms int, config *RealisConfig) (*RealisCon
 
 	httpTrans := (trans).(*thrift.THttpClient)
 	httpTrans.SetHeader("Content-Type", "application/x-thrift")
-	httpTrans.SetHeader("User-Agent", "GoRealis v"+VERSION)
+	httpTrans.SetHeader("User-Agent", "gorealis v"+VERSION)
 
 	return &RealisConfig{transport: trans, protoFactory: thrift.NewTJSONProtocolFactory()}, nil
 }
@@ -460,7 +464,7 @@ func newTBinaryConfig(url string, timeoutms int, config *RealisConfig) (*RealisC
 
 	httpTrans.SetHeader("Accept", "application/vnd.apache.thrift.binary")
 	httpTrans.SetHeader("Content-Type", "application/vnd.apache.thrift.binary")
-	httpTrans.SetHeader("User-Agent", "GoRealis v"+VERSION)
+	httpTrans.SetHeader("User-Agent", "gorealis v"+VERSION)
 
 	return &RealisConfig{transport: trans, protoFactory: thrift.NewTBinaryProtocolFactoryDefault()}, nil
 
@@ -476,6 +480,9 @@ func (r *realisClient) ReestablishConn() error {
 	r.logger.Println("Re-establishing Connection to Aurora")
 	r.Close()
 
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
 	// Recreate connection from scratch using original options
 	newRealis, err := NewRealisClient(r.config.options...)
 	if err != nil {
@@ -498,6 +505,10 @@ func (r *realisClient) ReestablishConn() error {
 
 // Releases resources associated with the realis client.
 func (r *realisClient) Close() {
+
+	r.lock.Lock()
+	defer r.lock.Unlock()
+
 	r.client.Transport.Close()
 	r.readonlyClient.Transport.Close()
 	r.adminClient.Transport.Close()
@@ -555,14 +566,14 @@ func (r *realisClient) GetJobs(role string) (*aurora.Response, *aurora.GetJobsRe
 		return r.readonlyClient.GetJobs(role)
 	})
 
-	if resp.GetResult_() != nil {
-		result = resp.GetResult_().GetJobsResult_
-	}
-
 	if retryErr != nil {
 		return nil, result, errors.Wrap(retryErr, "Error getting Jobs from Aurora Scheduler")
 	}
 
+	if resp.GetResult_() != nil {
+		result = resp.GetResult_().GetJobsResult_
+	}
+
 	return resp, result, nil
 }
 
@@ -635,7 +646,7 @@ func (r *realisClient) CreateService(auroraJob Job, settings *aurora.JobUpdateSe
 		return resp, nil, errors.Wrap(err, "unable to create service")
 	}
 
-	if resp != nil && resp.GetResult_() != nil {
+	if resp.GetResult_() != nil {
 		return resp, resp.GetResult_().GetStartJobUpdateResult_(), nil
 	}
 
@@ -879,7 +890,7 @@ func (r *realisClient) GetPendingReason(query *aurora.TaskQuery) (pendingReasons
 
 	var result map[*aurora.PendingReason]bool
 
-	if resp != nil && resp.GetResult_() != nil {
+	if resp.GetResult_() != nil {
 		result = resp.GetResult_().GetGetPendingReasonResult_().GetReasons()
 	}
 	for reason := range result {
@@ -999,14 +1010,14 @@ func (r *realisClient) DrainHosts(hosts ...string) (*aurora.Response, *aurora.Dr
 		return r.adminClient.DrainHosts(drainList)
 	})
 
-	if resp != nil && resp.GetResult_() != nil {
-		result = resp.GetResult_().GetDrainHostsResult_()
-	}
-
 	if retryErr != nil {
 		return resp, result, errors.Wrap(retryErr, "Unable to recover connection")
 	}
 
+	if resp.GetResult_() != nil {
+		result = resp.GetResult_().GetDrainHostsResult_()
+	}
+
 	return resp, result, nil
 }
 
@@ -1030,14 +1041,14 @@ func (r *realisClient) StartMaintenance(hosts ...string) (*aurora.Response, *aur
 		return r.adminClient.StartMaintenance(hostList)
 	})
 
-	if resp.GetResult_() != nil {
-		result = resp.GetResult_().GetStartMaintenanceResult_()
-	}
-
 	if retryErr != nil {
 		return resp, result, errors.Wrap(retryErr, "Unable to recover connection")
 	}
 
+	if resp.GetResult_() != nil {
+		result = resp.GetResult_().GetStartMaintenanceResult_()
+	}
+
 	return resp, result, nil
 }
 
@@ -1061,14 +1072,14 @@ func (r *realisClient) EndMaintenance(hosts ...string) (*aurora.Response, *auror
 		return r.adminClient.EndMaintenance(hostList)
 	})
 
-	if resp.GetResult_() != nil {
-		result = resp.GetResult_().GetEndMaintenanceResult_()
-	}
-
 	if retryErr != nil {
 		return resp, result, errors.Wrap(retryErr, "Unable to recover connection")
 	}
 
+	if resp.GetResult_() != nil {
+		result = resp.GetResult_().GetEndMaintenanceResult_()
+	}
+
 	return resp, result, nil
 }
 
@@ -1094,14 +1105,14 @@ func (r *realisClient) MaintenanceStatus(hosts ...string) (*aurora.Response, *au
 		return r.adminClient.MaintenanceStatus(hostList)
 	})
 
-	if resp.GetResult_() != nil {
-		result = resp.GetResult_().GetMaintenanceStatusResult_()
-	}
-
 	if retryErr != nil {
 		return resp, result, errors.Wrap(retryErr, "Unable to recover connection")
 	}
 
+	if resp.GetResult_() != nil {
+		result = resp.GetResult_().GetMaintenanceStatusResult_()
+	}
+
 	return resp, result, nil
 }
 

retry.go

@@ -15,9 +15,12 @@
 package realis
 
 import (
+	"io"
 	"math/rand"
+	"net/url"
 	"time"
 
+	"git.apache.org/thrift.git/lib/go/thrift"
 	"github.com/paypal/gorealis/gen-go/apache/aurora"
 	"github.com/paypal/gorealis/response"
 	"github.com/pkg/errors"
@@ -88,7 +91,6 @@ func ExponentialBackoff(backoff Backoff, logger Logger, condition ConditionFunc)
 		}
 
 		if err != nil {
-
 			// If the error is temporary, continue retrying.
 			if !IsTemporary(err) {
 				return err
@@ -96,9 +98,7 @@ func ExponentialBackoff(backoff Backoff, logger Logger, condition ConditionFunc)
 				// Print out the temporary error we experienced.
 				logger.Println(err)
 			}
-
 		}
-
 	}
 
 	if curStep > 1 {
@@ -158,6 +158,22 @@ func (r *realisClient) thriftCallWithRetries(thriftCall auroraThriftCall) (*auro
 			// Print out the error to the user
 			r.logger.Printf("Client Error: %v\n", clientErr)
 
+			// Determine if error is a temporary URL error by going up the stack
+			e, ok := clientErr.(thrift.TTransportException)
+			if ok {
+				r.logger.DebugPrint("Encountered a transport exception")
+
+				e, ok := e.Err().(*url.Error)
+				if ok {
+					// EOF error occurs when the server closes the read buffer of the client. This is common
+					// when the server is overloaded and should be retried. All other errors that are permanent
+					// will not be retried.
+					if e.Err != io.EOF && !e.Temporary() {
+						return nil, errors.Wrap(clientErr, "Permanent connection error")
+					}
+				}
+			}
+
 			// In the future, reestablish connection should be able to check if it is actually possible
 			// to make a thrift call to Aurora. For now, a reconnect should always lead to a retry.
 			r.ReestablishConn()