20540: Implement nearly-full jitter for exponential backoff.

[arvados.git] / sdk / go / arvados / client.go

diff --git a/sdk/go/arvados/client.go b/sdk/go/arvados/client.go
index 6316d1bedaceb35bc7d3f5578aff3425078aabb7..c4031465034a9e792c46ffbcb5ae1445fbe70230 100644 (file)
--- a/sdk/go/arvados/client.go
+++ b/sdk/go/arvados/client.go
@@ -16,12 +16,15 @@ import (
        "io/fs"
        "io/ioutil"
        "log"
+       "math"
        "math/big"
+       mathrand "math/rand"
        "net"
        "net/http"
        "net/url"
        "os"
        "regexp"
+       "strconv"
        "strings"
        "sync/atomic"
        "time"
@@ -274,6 +277,7 @@ func (c *Client) Do(req *http.Request) (*http.Response, error) {
 
        rclient := retryablehttp.NewClient()
        rclient.HTTPClient = c.httpClient()
+       rclient.Backoff = exponentialBackoff
        if c.Timeout > 0 {
                rclient.RetryWaitMax = c.Timeout / 10
                rclient.RetryMax = 32
@@ -370,6 +374,35 @@ func isRedirectStatus(code int) bool {
        }
 }
 
+// Implements retryablehttp.Backoff using the server-provided
+// Retry-After header if available, otherwise nearly-full jitter
+// exponential backoff (similar to
+// https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/),
+// in all cases respecting the provided min and max.
+func exponentialBackoff(min, max time.Duration, attemptNum int, resp *http.Response) time.Duration {
+       var t time.Duration
+       if resp != nil && (resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode == http.StatusServiceUnavailable) {
+               if s := resp.Header.Get("Retry-After"); s != "" {
+                       if sleep, err := strconv.ParseInt(s, 10, 64); err == nil {
+                               t = time.Second * time.Duration(sleep)
+                       } else if stamp, err := time.Parse(time.RFC1123, s); err == nil {
+                               t = stamp.Sub(time.Now())
+                       }
+               }
+       }
+       if t == 0 {
+               jitter := mathrand.New(mathrand.NewSource(int64(time.Now().Nanosecond()))).Float64()
+               t = min + time.Duration((math.Pow(2, float64(attemptNum))*float64(min)-float64(min))*jitter)
+       }
+       if t < min {
+               return min
+       } else if t > max {
+               return max
+       } else {
+               return t
+       }
+}
+
 // DoAndDecode performs req and unmarshals the response (which must be
 // JSON) into dst. Use this instead of RequestAndDecode if you need
 // more control of the http.Request object.