feat(config): Add env/file support to Worker.Controllers field

This feature allows the user to set the `controllers` field to a string
that points to either an environment variable or file.
We then dynamically pull out the value and parse it into the config.

CHANGELOG.md

@@ -5,13 +5,16 @@ Canonical reference for changes, improvements, and bugfixes for Boundary.
 ## Next
 
 ### New and Improved
+
 * config: The `execution_dir` field for plugins now supports being set from environment variables
   or a file on disk.([PR](https://github.com/hashicorp/boundary/pull/1772))
+* config: Add support for reading worker controllers off of environment
+  variables as well as files. ([PR](https://github.com/hashicorp/boundary/pull/1765))
 * config: The `description` field for controllers now supports being set
   from environment variables or a file on disk
   ([PR](https://github.com/hashicorp/boundary/pull/1766))
 * config: Add support for reading worker tags off of environment variables
-as well as files. ([PR](https://github.com/hashicorp/boundary/pull/1758))
+  as well as files. ([PR](https://github.com/hashicorp/boundary/pull/1758))
 * config: Add support for go-sockaddr templates to Worker and Controller
   addresses. ([PR](https://github.com/hashicorp/boundary/pull/1731))
 * host: Plugin-based host catalogs will now schedule updates for all

internal/cmd/config/config.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"reflect"
 	"strings"
 	"time"
 
@@ -151,10 +152,15 @@ func (c *Controller) InitNameIfEmpty() (string, error) {
 }
 
 type Worker struct {
-	Name        string   `hcl:"name"`
-	Description string   `hcl:"description"`
-	Controllers []string `hcl:"controllers"`
-	PublicAddr  string   `hcl:"public_addr"`
+	Name        string `hcl:"name"`
+	Description string `hcl:"description"`
+	PublicAddr  string `hcl:"public_addr"`
+
+	// We use a raw interface here so that we can take in a string
+	// value pointing to an env var or file. We then resolve that
+	// and get the actual controller addresses.
+	Controllers    []string    `hcl:"-"`
+	ControllersRaw interface{} `hcl:"controllers"`
 
 	// We use a raw interface for parsing so that people can use JSON-like
 	// syntax that maps directly to the filter input or possibly more familiar
@@ -448,6 +454,11 @@ func Parse(d string) (*Config, error) {
 				}
 			}
 		}
+
+		result.Worker.Controllers, err = parseWorkerControllers(result)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to parse worker controllers: %w", err)
+		}
 	}
 
 	sharedConfig, err := configutil.ParseConfig(d)
@@ -506,6 +517,42 @@ func Parse(d string) (*Config, error) {
 	return result, nil
 }
 
+func parseWorkerControllers(c *Config) ([]string, error) {
+	if c == nil || c.Worker == nil {
+		return nil, fmt.Errorf("config or worker field is nil")
+	}
+	if c.Worker.ControllersRaw == nil {
+		return nil, nil
+	}
+
+	switch t := c.Worker.ControllersRaw.(type) {
+	case []interface{}: // An array was configured directly in Boundary's HCL Config file.
+		var controllers []string
+		err := mapstructure.WeakDecode(c.Worker.ControllersRaw, &controllers)
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode worker controllers block into config field: %w", err)
+		}
+		return controllers, nil
+
+	case string:
+		controllersStr, err := parseutil.ParsePath(t)
+		if err != nil {
+			return nil, fmt.Errorf("bad env var or file pointer: %w", err)
+		}
+
+		var addrs []string
+		err = json.Unmarshal([]byte(controllersStr), &addrs)
+		if err != nil {
+			return nil, fmt.Errorf("failed to unmarshal env/file contents: %w", err)
+		}
+		return addrs, nil
+
+	default:
+		typ := reflect.TypeOf(t)
+		return nil, fmt.Errorf("unexpected type %q", typ.String())
+	}
+}
+
 func parseEventing(eventObj *ast.ObjectItem) (*event.EventerConfig, error) {
 	// Decode the outside struct
 	var result event.EventerConfig

internal/cmd/config/config_test.go

@@ -9,6 +9,7 @@ import (
 	"github.com/hashicorp/boundary/internal/observability/event"
 	"github.com/hashicorp/go-secure-stdlib/configutil"
 	"github.com/hashicorp/go-secure-stdlib/listenerutil"
+	"github.com/hashicorp/go-secure-stdlib/parseutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -173,9 +174,10 @@ func TestDevWorker(t *testing.T) {
 			},
 		},
 		Worker: &Worker{
-			Name:        "dev-worker",
-			Description: "A default worker created in dev mode",
-			Controllers: []string{"127.0.0.1"},
+			Name:           "dev-worker",
+			Description:    "A default worker created in dev mode",
+			Controllers:    []string{"127.0.0.1"},
+			ControllersRaw: []interface{}{"127.0.0.1"},
 			Tags: map[string][]string{
 				"type": {"dev", "local"},
 			},
@@ -811,6 +813,146 @@ func TestController_EventingConfig(t *testing.T) {
 	}
 }
 
+func TestWorkerControllers(t *testing.T) {
+	tests := []struct {
+		name                 string
+		in                   string
+		stateFn              func(t *testing.T)
+		expWorkerControllers []string
+		expErr               bool
+		expErrIs             error
+		expErrStr            string
+	}{
+		{
+			name: "No Controllers",
+			in: `
+			worker {
+				name = "test"
+			}
+			`,
+			expWorkerControllers: nil,
+			expErr:               false,
+		},
+		{
+			name: "One Controller",
+			in: `
+			worker {
+				name = "test"
+				controllers = ["127.0.0.1"]
+			}
+			`,
+			expWorkerControllers: []string{"127.0.0.1"},
+			expErr:               false,
+		},
+		{
+			name: "Multiple controllers",
+			in: `
+			worker {
+				name = "test"
+				controllers = ["127.0.0.1", "127.0.0.2", "127.0.0.3"]
+			}
+			`,
+			expWorkerControllers: []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"},
+			expErr:               false,
+		},
+		{
+			name: "Using env var",
+			in: `
+			worker {
+				name = "test"
+				controllers = "env://BOUNDARY_WORKER_CONTROLLERS"
+			}
+			`,
+			stateFn:              func(t *testing.T) { t.Setenv("BOUNDARY_WORKER_CONTROLLERS", `["127.0.0.1", "127.0.0.2", "127.0.0.3"]`) },
+			expWorkerControllers: []string{"127.0.0.1", "127.0.0.2", "127.0.0.3"},
+			expErr:               false,
+		},
+		{
+			name: "Using env var - invalid input 1",
+			in: `
+			worker {
+				name = "test"
+				controllers = "env://BOUNDARY_WORKER_CONTROLLERS"
+			}
+			`,
+			stateFn: func(t *testing.T) {
+				controllers := `
+				worker {
+					controllers = ["127.0.0.1"]
+				}
+				`
+				t.Setenv("BOUNDARY_WORKER_CONTROLLERS", controllers)
+			},
+			expWorkerControllers: nil,
+			expErr:               true,
+			expErrStr:            "Failed to parse worker controllers: failed to unmarshal env/file contents: invalid character 'w' looking for beginning of value",
+		},
+		{
+			name: "Using env var - invalid input 2",
+			in: `
+			worker {
+				name = "test"
+				controllers = "env://BOUNDARY_WORKER_CONTROLLERS"
+			}
+			`,
+			stateFn:              func(t *testing.T) { t.Setenv("BOUNDARY_WORKER_CONTROLLERS", `controllers = ["127.0.0.1"]`) },
+			expWorkerControllers: nil,
+			expErr:               true,
+			expErrStr:            "Failed to parse worker controllers: failed to unmarshal env/file contents: invalid character 'c' looking for beginning of value",
+		},
+		{
+			name: "Unsupported object",
+			in: `
+			worker {
+				name = "test"
+				controllers = {
+					ip = "127.0.0.1"
+					ip = "127.0.0.2"
+				}
+			}
+			`,
+			expWorkerControllers: nil,
+			expErr:               true,
+			expErrStr:            "Failed to parse worker controllers: unexpected type \"[]map[string]interface {}\"",
+		},
+		{
+			name: "worker controllers set to invalid url",
+			in: `
+			worker {
+				name = "test"
+				controllers = "env://\x00"
+			}`,
+			expWorkerControllers: nil,
+			expErr:               true,
+			expErrIs:             parseutil.ErrNotAUrl,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.stateFn != nil {
+				tt.stateFn(t)
+			}
+
+			c, err := Parse(tt.in)
+			if tt.expErr {
+				if tt.expErrIs != nil {
+					require.ErrorIs(t, err, tt.expErrIs)
+				} else {
+					require.EqualError(t, err, tt.expErrStr)
+				}
+				require.Nil(t, c)
+				return
+			}
+
+			require.NoError(t, err)
+			require.NotNil(t, c)
+			require.NotNil(t, c.Worker)
+			require.EqualValues(t, tt.expWorkerControllers, c.Worker.Controllers)
+		})
+	}
+}
+
 func TestControllerDescription(t *testing.T) {
 	tests := []struct {
 		name           string

website/content/docs/configuration/worker.mdx

@@ -34,7 +34,11 @@ worker {
   or a [go-sockaddr template](https://godoc.org/github.com/hashicorp/go-sockaddr/template).
 
 - `controllers` - A list of hosts/IP addresses and optionally ports for reaching
-  controllers. The port will default to :9201 if not specified.
+  controllers. The port will default to :9201 if not specified. This value can be
+  a direct access string array with the addresses, or it can refer to a file on
+  disk (file://) from which the addresses will be read, or an env var (env://) from
+  which the addresses will be read. When using env or file, their contents
+  must formatted as a JSON array: `["127.0.0.1", "192.168.0.1", "10.0.0.1"]`
 
 - `tags` - A map of key-value pairs where values are an array of strings. Most
   commonly used for [filtering](/docs/concepts/filtering) targets a worker can