physical/posgresql: add ability to prefer VAULT_PG_CONNECTION_URL envar over config file

physical/postgresql/configure.go

@@ -0,0 +1,21 @@
+package postgresql
+
+import (
+	"os"
+)
+
+// connectionURL first check the environment variables for a connection URL. If
+// no connection URL exists in the environment variable, the Vault config file is
+// checked. If neither the environment variables or the config file set the connection
+// URL for the Postgres backend, because it is a required field, an error is returned.
+func connectionURL(conf map[string]string) string {
+	connURL := os.Getenv("PG_CONNECTION_URL")
+	if connURL == "" {
+		connURL = conf["connection_url"]
+		if connURL == "" {
+			return ""
+		}
+	}
+
+	return connURL
+}

physical/postgresql/configure_test.go

@@ -0,0 +1,65 @@
+package postgresql
+
+import (
+	"os"
+	"testing"
+)
+
+func TestConnectionURL(t *testing.T) {
+	type input struct {
+		envar string
+		conf  map[string]string
+	}
+
+	var cases = []struct {
+		name  string
+		want  string
+		input input
+	}{
+		{
+			name: "environment_variable_not_set_use_config_value",
+			want: "abc",
+			input: input{
+				envar: "",
+				conf:  map[string]string{"connection_url": "abc"},
+			},
+		},
+		{
+			name: "no_value_connection_url_set_key_exists",
+			want: "",
+			input: input{
+				envar: "",
+				conf:  map[string]string{"connection_url": ""},
+			},
+		},
+		{
+			name: "no_value_connection_url_set_key_doesnt_exist",
+			want: "",
+			input: input{
+				envar: "",
+				conf:  map[string]string{},
+			},
+		},
+		{
+			name: "environment_variable_set",
+			want: "abc",
+			input: input{
+				envar: "abc",
+				conf:  map[string]string{"connection_url": "def"},
+			},
+		},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			os.Setenv("PG_CONNECTION_URL", tt.input.envar)
+			defer os.Setenv("PG_CONNECTION_URL", "")
+
+			got := connectionURL(tt.input.conf)
+
+			if got != tt.want {
+				t.Errorf("connectionURL(%s): want '%s', got '%s'", tt.input, tt.want, got)
+			}
+		})
+	}
+}

physical/postgresql/postgresql.go

@@ -88,8 +88,8 @@ type PostgreSQLLock struct {
 // API client, server address, credentials, and database.
 func NewPostgreSQLBackend(conf map[string]string, logger log.Logger) (physical.Backend, error) {
 	// Get the PostgreSQL credentials to perform read/write operations.
-	connURL, ok := conf["connection_url"]
-	if !ok || connURL == "" {
+	connURL := connectionURL(conf)
+	if connURL == "" {
 		return nil, fmt.Errorf("missing connection_url")
 	}
 

website/source/docs/configuration/storage/postgresql.html.md

@@ -93,7 +93,8 @@ LANGUAGE plpgsql;
 ## `postgresql` Parameters
 
 - `connection_url` `(string: <required>)` – Specifies the connection string to
-  use to authenticate and connect to PostgreSQL. A full list of supported
+  use to authenticate and connect to PostgreSQL. The connection URL can also be
+  set using the `PG_CONNECTION_URL` environment variable. A full list of supported
   parameters can be found in [the pq library documentation][pglib]. For example
   connection string URLs, see the examples section below.