gorealis/retry.go

/**
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package realis

import (
	"io"
	"math/rand"
	"net/url"
	"time"

	"github.com/apache/thrift/lib/go/thrift"
	"github.com/paypal/gorealis/gen-go/apache/aurora"
	"github.com/paypal/gorealis/response"
	"github.com/pkg/errors"
)

type Backoff struct {
	Duration time.Duration // the base duration
	Factor   float64       // Duration is multiplied by a factor each iteration
	Jitter   float64       // The amount of jitter applied each iteration
	Steps    int           // Exit with error after this many steps
}

// Jitter returns a time.Duration between duration and duration + maxFactor *
// duration.
//
// This allows clients to avoid converging on periodic behavior. If maxFactor
// is 0.0, a suggested default value will be chosen.
func Jitter(duration time.Duration, maxFactor float64) time.Duration {
	if maxFactor <= 0.0 {
		maxFactor = 1.0
	}
	wait := duration + time.Duration(rand.Float64()*maxFactor*float64(duration))
	return wait
}

// ConditionFunc returns true if the condition is satisfied, or an error
// if the loop should be aborted.
type ConditionFunc func() (done bool, err error)

// Modified version of the Kubernetes exponential-backoff code.
// ExponentialBackoff repeats a condition check with exponential backoff.
//
// It checks the condition up to Steps times, increasing the wait by multiplying
// the previous duration by Factor.
//
// If Jitter is greater than zero, a random amount of each duration is added
// (between duration and duration*(1+jitter)).
//
// If the condition never returns true, ErrWaitTimeout is returned. Errors
// do not cause the function to return.

func ExponentialBackoff(backoff Backoff, logger Logger, condition ConditionFunc) error {
	var err error
	var ok bool
	var curStep int
	duration := backoff.Duration

	for curStep = 0; curStep < backoff.Steps; curStep++ {

		// Only sleep if it's not the first iteration.
		if curStep != 0 {
			adjusted := duration
			if backoff.Jitter > 0.0 {
				adjusted = Jitter(duration, backoff.Jitter)
			}

			logger.Printf("A retryable error occurred during function call, backing off for %v before retrying\n", adjusted)
			time.Sleep(adjusted)
			duration = time.Duration(float64(duration) * backoff.Factor)
		}

		// Execute function passed in.
		ok, err = condition()

		// If the function executed says it succeeded, stop retrying
		if ok {
			return nil
		}

		if err != nil {
			// If the error is temporary, continue retrying.
			if !IsTemporary(err) {
				return err
			} else {
				// Print out the temporary error we experienced.
				logger.Println(err)
			}
		}
	}

	if curStep > 1 {
		logger.Printf("retried this function call %d time(s)", curStep)
	}

	// Provide more information to the user wherever possible
	if err != nil {
		return newRetryError(errors.Wrap(err, "ran out of retries"), curStep)
	} else {
		return newRetryError(errors.New("ran out of retries"), curStep)
	}
}

type auroraThriftCall func() (resp *aurora.Response, err error)

// Duplicates the functionality of ExponentialBackoff but is specifically targeted towards ThriftCalls.
func (r *realisClient) thriftCallWithRetries(returnOnTimeout bool, thriftCall auroraThriftCall) (*aurora.Response, error) {
	var resp *aurora.Response
	var clientErr error
	var curStep int
	timeouts := 0

	backoff := r.config.backoff
	duration := backoff.Duration

	for curStep = 0; curStep < backoff.Steps; curStep++ {

		// If this isn't our first try, backoff before the next try.
		if curStep != 0 {
			adjusted := duration
			if backoff.Jitter > 0.0 {
				adjusted = Jitter(duration, backoff.Jitter)
			}

			r.logger.Printf("A retryable error occurred during thrift call, backing off for %v before retry %v\n", adjusted, curStep)

			time.Sleep(adjusted)
			duration = time.Duration(float64(duration) * backoff.Factor)
		}

		// Only allow one go-routine make use or modify the thrift client connection.
		// Placing this in an anonymous function in order to create a new, short-lived stack allowing unlock
		// to be run in case of a panic inside of thriftCall.
		func() {
			r.lock.Lock()
			defer r.lock.Unlock()

			resp, clientErr = thriftCall()

			r.logger.TracePrintf("Aurora Thrift Call ended resp: %v clientErr: %v\n", resp, clientErr)
		}()

		// Check if our thrift call is returning an error. This is a retryable event as we don't know
		// if it was caused by network issues.
		if clientErr != nil {

			// 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")
					}

					// Corner case where thrift payload was received by Aurora but connection timedout before Aurora was
					// able to reply. In this case we will return whatever response was received and a TimedOut behaving
					// error. Users can take special action on a timeout by using IsTimedout and reacting accordingly.
					if e.Timeout() {
						timeouts++
						r.logger.DebugPrintf(
							"Client closed connection (timedout) %d times before server responded, consider increasing connection timeout",
							timeouts)
						if returnOnTimeout {
							return resp, newTimedoutError(errors.New("client connection closed before server answer"))
						}
					}
				}
			}

			// 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()

		} else {

			// If there was no client error, but the response is nil, something went wrong.
			// Ideally, we'll never encounter this but we're placing a safeguard here.
			if resp == nil {
				return nil, errors.New("response from aurora is nil")
			}

			// Check Response Code from thrift and make a decision to continue retrying or not.
			switch responseCode := resp.GetResponseCode(); responseCode {

			// If the thrift call succeeded, stop retrying
			case aurora.ResponseCode_OK:
				return resp, nil

			// If the response code is transient, continue retrying
			case aurora.ResponseCode_ERROR_TRANSIENT:
				r.logger.Println("Aurora replied with Transient error code, retrying")
				continue

			// Failure scenarios, these indicate a bad payload or a bad config. Stop retrying.
			case aurora.ResponseCode_INVALID_REQUEST,
				aurora.ResponseCode_ERROR,
				aurora.ResponseCode_AUTH_FAILED,
				aurora.ResponseCode_JOB_UPDATING_ERROR:
				r.logger.Printf("Terminal Response Code %v from Aurora, won't retry\n", resp.GetResponseCode().String())
				return resp, errors.New(response.CombineMessage(resp))

				// The only case that should fall down to here is a WARNING response code.
				// It is currently not used as a response in the scheduler so it is unknown how to handle it.
			default:
				r.logger.DebugPrintf("unhandled response code %v received from Aurora\n", responseCode)
				return nil, errors.Errorf("unhandled response code from Aurora %v", responseCode.String())
			}
		}

	}

	r.logger.DebugPrintf("it took %v retries to complete this operation\n", curStep)

	if curStep > 1 {
		r.config.logger.Printf("retried this thrift call %d time(s)", curStep)
	}

	// Provide more information to the user wherever possible.
	if clientErr != nil {
		return nil, newRetryError(errors.Wrap(clientErr, "ran out of retries, including latest error"), curStep)
	} else {
		return nil, newRetryError(errors.New("ran out of retries"), curStep)
	}
}