fingerprint: Add retry and failure config to env fingerprinters.

.changelog/27161.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+client: Added a new `fingerprint` configuration block which allows users to specify retry behavior for the `env_aws`, `env_azure`, `env_digitalocean` and `env_gcp` fingerprinters.
+```

client/config/config.go

@@ -395,6 +395,10 @@ type Config struct {
 
 	// LogFile is used by MonitorExport to stream a server's log file
 	LogFile string `hcl:"log_file"`
+
+	// Fingerprinters is a map of fingerprinter configurations by name. This
+	// currently only applies to env fingerprinters such as "env_aws".
+	Fingerprinters map[string]*Fingerprint
 }
 
 type APIListenerRegistrar interface {
@@ -931,6 +935,7 @@ func DefaultConfig() *Config {
 			MinDynamicUser: 80_000,
 			MaxDynamicUser: 89_999,
 		},
+		Fingerprinters: map[string]*Fingerprint{},
 	}
 
 	return cfg

client/config/fingerprint.go

@@ -0,0 +1,120 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: BUSL-1.1
+
+package config
+
+import (
+	"errors"
+	"fmt"
+	"slices"
+	"strings"
+	"time"
+)
+
+// validEnvFingerprinters contains the fingerprinters that are valid
+// environment fingerprinters and is used for input validation.
+var validEnvFingerprinters = []string{
+	"env_aws",
+	"env_azure",
+	"env_gce",
+	"env_digitalocean",
+}
+
+// Fingerprint is an optional configuration block for environment fingerprinters
+// can control retry behavior and failure handling.
+type Fingerprint struct {
+
+	// Name is the fingerprinter identifier that this configuration block
+	// relates to. It is gathered from the HCL block label.
+	Name string `hcl:",key"`
+
+	// RetryInterval specifies the time to wait between fingerprint
+	// attempts.
+	RetryInterval    time.Duration
+	RetryIntervalHCL string `hcl:"retry_interval,optional"`
+
+	// RetryAttempts specifies the maximum number of fingerprint attempts to be
+	// made before the failure is considered terminal.
+	RetryAttempts int `hcl:"retry_attempts,optional"`
+
+	// ExitOnFailure indicates whether the fingerprinter should cause the agent
+	// to exit if it fails to correctly perform its fingerprint run. This is
+	// useful if the fingerprinter provides critical information used by Nomad
+	// workloads.
+	ExitOnFailure *bool `hcl:"exit_on_failure,optional"`
+
+	// ExtraKeysHCL is used by hcl to surface unexpected keys
+	ExtraKeysHCL []string `hcl:",unusedKeys" json:"-"`
+}
+
+// Copy is used to satisfy to helper.Copyable interface, so we can perform
+// copies of the fingerprint config slice.
+func (f *Fingerprint) Copy() *Fingerprint {
+	if f == nil {
+		return nil
+	}
+
+	c := new(Fingerprint)
+	*c = *f
+	return c
+}
+
+// Merge is used to combine two fingerprint blocks with the block passed into
+// the function taking precedence. The name is not overwritten as this is
+// expected to match as it's the block label. It is the callers responsibility
+// to ensure the two fingerprint blocks are for the same fingerprinter
+// implementation.
+func (f *Fingerprint) Merge(z *Fingerprint) *Fingerprint {
+	if f == nil {
+		return z
+	}
+
+	result := *f
+
+	if z == nil {
+		return &result
+	}
+
+	if z.RetryInterval != 0 {
+		result.RetryInterval = z.RetryInterval
+	}
+	if z.RetryIntervalHCL != "" {
+		result.RetryIntervalHCL = z.RetryIntervalHCL
+	}
+	if z.RetryAttempts != 0 {
+		result.RetryAttempts = z.RetryAttempts
+	}
+	if z.ExitOnFailure != nil {
+		result.ExitOnFailure = z.ExitOnFailure
+	}
+
+	return &result
+}
+
+// Validate the fingerprint block to ensure we do not have any values that
+// cannot be handled.
+func (f *Fingerprint) Validate() error {
+
+	if f == nil {
+		return nil
+	}
+
+	if f.Name == "" {
+		return errors.New("fingerprint name cannot be empty")
+	}
+	if !slices.Contains(validEnvFingerprinters, f.Name) {
+		return fmt.Errorf("fingerprint %q does not support configuration", f.Name)
+	}
+	if f.RetryInterval < 0 {
+		return fmt.Errorf("fingerprint %q retry interval cannot be negative", f.Name)
+	}
+	if f.RetryAttempts < -1 {
+		return fmt.Errorf("fingerprint %q retry attempts cannot be less than -1", f.Name)
+	}
+	if len(f.ExtraKeysHCL) > 0 {
+		return fmt.Errorf("fingerprint %q contains unknown configuration options: %s",
+			f.Name, strings.Join(f.ExtraKeysHCL, ","))
+	}
+
+	return nil
+}