Make external provider less opinionated about executable

You can now specify the absolute path to a provider executable instead
of specifying a provider directory with a "garm-external-provider" in it.

config/external.go

@@ -38,14 +38,22 @@ type External struct {
 	// ProviderDir is the path on disk to a folder containing an executable
 	// called "garm-external-provider".
 	ProviderDir string `toml:"provider_dir" json:"provider-dir"`
+	// ProviderExecutable is the full path to the executable that implements
+	// the provider. If specified, it will take precedence over the "garm-external-provider"
+	// executable in the ProviderDir.
+	ProviderExecutable string `toml:"provider_executable" json:"provider-executable"`
 }
 
 func (e *External) ExecutablePath() (string, error) {
-	execPath := filepath.Join(e.ProviderDir, "garm-external-provider")
+	execPath := e.ProviderExecutable
+	if execPath == "" {
+		execPath = filepath.Join(e.ProviderDir, "garm-external-provider")
+	}
+
 	if !filepath.IsAbs(execPath) {
 		return "", fmt.Errorf("executable path must be an absolute path")
 	}
-	return filepath.Join(e.ProviderDir, "garm-external-provider"), nil
+	return execPath, nil
 }
 
 func (e *External) Validate() error {
@@ -58,14 +66,6 @@ func (e *External) Validate() error {
 		}
 	}
 
-	if e.ProviderDir == "" {
-		return fmt.Errorf("missing provider dir")
-	}
-
-	if !filepath.IsAbs(e.ProviderDir) {
-		return fmt.Errorf("path to provider dir must be absolute")
-	}
-
 	execPath, err := e.ExecutablePath()
 	if err != nil {
 		return errors.Wrap(err, "fetching executable path")

config/external_test.go

@@ -72,20 +72,20 @@ func TestExternal(t *testing.T) {
 			errString: "failed to access config file /there/is/no/config/here",
 		},
 		{
-			name: "Missing provider dir",
-			cfg: External{
-				ConfigFile:  "",
-				ProviderDir: "",
-			},
-			errString: "missing provider dir",
-		},
-		{
-			name: "Provider dir must not be relative",
+			name: "Provider dir path must be absolute",
 			cfg: External{
 				ConfigFile:  "",
 				ProviderDir: "../test",
 			},
-			errString: "path to provider dir must be absolute",
+			errString: "fetching executable path: executable path must be an absolute path",
+		},
+		{
+			name: "Provider executable path must be absolute",
+			cfg: External{
+				ConfigFile:         "",
+				ProviderExecutable: "../test",
+			},
+			errString: "fetching executable path: executable path must be an absolute path",
 		},
 		{
 			name: "Provider executable not found",

contrib/providers.d/openstack/README.md

@@ -2,4 +2,11 @@
 
 This is an example external provider, written for OpenStack. It is a simple bash script that implements the external provider interface, in order to supply ```garm``` with compute instances. This is just an example, complete with a sample config file.
 
-Not all functions are implemented, just the bare minimum to get it to work with the current feature set of ```garm```. It is not meant for production, as it needs a lot more error checking, retries, and potentially more flexibility to be of any use in a real environment.
+Not all functions are implemented, just the bare minimum to get it to work with the current feature set of ```garm```. It is not meant for production, as it needs a lot more error checking, retries, and potentially more flexibility to be of any use in a real environment.
+
+Images that are used with garm require the following properties set on the image:
+
+  * os_type (one of: windows, linux)
+  * os_distro
+  * os_version
+  * architecture (one of: x86_64, armv7l, mips64, mips64el, mips, mipsel)

contrib/providers.d/openstack/garm-external-provider

@@ -275,7 +275,11 @@ function CreateInstance() {
     checkValNotNull "${VERSION}" "os_version" || return $?
     ARCH=$(echo "${IMAGE_DETAILS}" | jq -c -r '.properties.architecture')
     checkValNotNull "${ARCH}" "architecture" || return $?
+    GH_ARCH=OS_TO_GH_ARCH_MAP[${ARCH}]
 
+    if [ -z "${GH_ARCH}" ];then
+        GH_ARCH=${ARCH}
+    fi
 
     SOURCE_ARGS=""
 
@@ -327,7 +331,7 @@ function CreateInstance() {
         --arg OS_TYPE "${OS_TYPE}" \
         --arg OS_NAME "${DISTRO}" \
         --arg OS_VERSION "${VERSION}" \
-        --arg ARCH "${ARCH}" \
+        --arg ARCH "${GH_ARCH}" \
         --arg STATUS "${STATUS_MAP[${STATUS}]}" \
         --arg POOL_ID "${GARM_POOL_ID}" \
         --arg FAULT "${FAULT_VAL}" \

testdata/config.toml

@@ -170,9 +170,10 @@ provider_type = "external"
   [provider.external]
   # config file passed to the executable via GARM_PROVIDER_CONFIG_FILE environment variable
   config_file = "/etc/garm/providers.d/azure/config.sh"
-  # path on disk to a folder that contains a "garm-external-provider" executable. The executable
-  # can be anything (bash, a binary, python, etc)
-  provider_dir = "/etc/garm/providers.d/azure"
+  # Absolute path to an executable that implements the provider logic. This executable can be
+  # anything (bash, a binary, python, etc). See documentation in this repo on how to write an
+  # external provider.
+  provider_executable = "/etc/garm/providers.d/azure/garm-external-provider"
 
 # This is a list of credentials that you can define as part of the repository
 # or organization definitions. They are not saved inside the database, as there