Remove bucket_patterns param

This can be achieved in prometheus with a relabel_config.

README.md

@@ -116,35 +116,37 @@ exporter has access to.
 
 This should be all the config required to successfully scrape every bucket:
 
-```
+```yml
 scrape_configs:
-  - job_name: 's3'
+  - job_name: "s3"
     metrics_path: /probe
     http_sd_configs:
       - url: http://127.0.0.1:9340/discovery
 ```
 
-You can limit the buckets returned with the `bucket_pattern` parameter. Refer to
-the documentation for [`path.Match`](https://golang.org/pkg/path/#Match) for the
-pattern syntax.
+Use `relabel_configs` to select the buckets you want to scrape:
 
-```
+```yml
 scrape_configs:
-  - job_name: 's3'
+  - job_name: "s3"
     metrics_path: /probe
     http_sd_configs:
-      # This will only discover buckets with a name that starts with example-
-      - url: http://127.0.0.1:9340/discovery?bucket_pattern=example-*
+      - url: http://127.0.0.1:9340/discovery
+    relabel_configs:
+      # Keep buckets that start with example-
+      - source_labels: [__param_bucket]
+        action: keep
+        regex: ^example-.*
 ```
 
 The prefix can be set too, but be mindful that this will apply to all buckets:
 
-```
+```yml
 scrape_configs:
-  - job_name: 's3'
+  - job_name: "s3"
     metrics_path: /probe
     http_sd_configs:
-      - url: http://127.0.0.1:9340/discovery?bucket_pattern=example-*
+      - url: http://127.0.0.1:9340/discovery
     params:
       prefix: ["thing.txt"]
 ```

s3_exporter.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"net/http"
 	"os"
-	"path"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -173,27 +172,17 @@ type discoveryTarget struct {
 }
 
 func discoveryHandler(w http.ResponseWriter, r *http.Request, svc s3iface.S3API) {
-	// If a bucket pattern isn't specified, then return every bucket
-	bucketPattern := r.URL.Query().Get("bucket_pattern")
-	if bucketPattern == "" {
-		bucketPattern = "*"
-	}
-
 	result, err := svc.ListBuckets(&s3.ListBucketsInput{})
 	if err != nil {
+		log.Errorln(err)
 		http.Error(w, "error listing buckets", http.StatusInternalServerError)
 		return
 	}
 
 	targets := []discoveryTarget{}
 	for _, b := range result.Buckets {
 		name := aws.StringValue(b.Name)
-
-		matched, err := path.Match(bucketPattern, name)
-		if err != nil {
-			http.Error(w, "bad pattern provided for 'bucket_pattern'", http.StatusBadRequest)
-		}
-		if matched {
+		if name != "" {
 			t := discoveryTarget{
 				Targets: []string{r.Host},
 				Labels: map[string]string{