add a single target field to simplified playbook

README.md

@@ -274,6 +274,7 @@ Here are the main differences between the two types of playbooks:
 - The full playbook supports multiple tasks, while the simplified playbook only supports a single task. This means that the full playbook can execute multiple sets of commands, whereas the simplified playbook can only execute one set of commands.
 - The full playbook supports various target types, such as `hosts`, `groups`, and `names`, while the simplified playbook only supports a single type, which is a list of names or host addresses. See the [Targets](#targets) section for more details.
 - The simplified playbook does not support task-level `on_error`, `user`, and `ssh_key` fields, while the full playbook does. See the [Task details](#task-details) section for more information.
+- The simplified playbook also has `target` field (in addition to `targets`) allows to set a single host/name only. This is useful when user want to run the playbook on a single host only. The full playbook does not have this field.
 
 Both types of playbooks support the remaining fields and options.
 

pkg/config/playbook.go

@@ -47,6 +47,7 @@ type SimplePlayBook struct {
 	SSHKey    string   `yaml:"ssh_key" toml:"ssh_key"`     // ssh key
 	Inventory string   `yaml:"inventory" toml:"inventory"` // inventory file or url
 	Targets   []string `yaml:"targets" toml:"targets"`     // list of names
+	Target    string   `yaml:"target" toml:"target"`       // a single target to run task on
 	Task      []Cmd    `yaml:"task" toml:"task"`           // single task is a list of commands
 }
 
@@ -219,7 +220,7 @@ func unmarshalPlaybookFile(fname string, data []byte, overrides *Overrides, res
 	}
 
 	errors := new(multierror.Error)
-	if err = unmarshal(data, res); err == nil {
+	if err = unmarshal(data, res); err == nil && len(res.Tasks) > 0 {
 		return nil // success, this is full PlayBook config
 	}
 	errors = multierror.Append(errors, err)
@@ -232,8 +233,14 @@ func unmarshalPlaybookFile(fname string, data []byte, overrides *Overrides, res
 		res.Tasks[0].Name = "default"               // we have only one task, set it as default
 
 		hasInventory := simple.Inventory != "" || (overrides != nil && overrides.Inventory != "")
+
 		target := Target{}
-		for _, t := range simple.Targets {
+		targets := append([]string{}, simple.Targets...)
+		if simple.Target != "" {
+			targets = append(targets, simple.Target) // append target from simple playbook
+		}
+
+		for _, t := range targets {
 			if strings.Contains(t, ":") {
 				ip, port := splitIPAddress(t)
 				target.Hosts = append(target.Hosts, Destination{Host: ip, Port: port}) // set as hosts in case of ip:port

pkg/config/playbook_test.go

@@ -133,6 +133,18 @@ func TestPlaybook_New(t *testing.T) {
 			{Host: "127.0.0.1", Port: 2222}}, c.Targets["default"].Hosts)
 	})
 
+	t.Run("simple playbook with a single target set", func(t *testing.T) {
+		c, err := New("testdata/simple-playbook-single-target.yml", nil, nil)
+		require.NoError(t, err)
+		require.Equal(t, 1, len(c.Tasks), "1 task")
+		assert.Equal(t, "default", c.Tasks[0].Name, "task name")
+		assert.Equal(t, 5, len(c.Tasks[0].Commands), "5 commands")
+
+		assert.Equal(t, 1, len(c.Targets))
+		assert.Equal(t, 0, len(c.Targets["default"].Names))
+		assert.Equal(t, []Destination{{Host: "127.0.0.1", Port: 2222}}, c.Targets["default"].Hosts)
+	})
+
 	t.Run("playbook with secrets", func(t *testing.T) {
 		secProvider := &mocks.SecretProvider{
 			GetFunc: func(key string) (string, error) {

pkg/config/testdata/simple-playbook-single-target.yml

@@ -0,0 +1,37 @@
+user: app
+ssh_key: ~/.ssh/id_rsa
+
+target: "127.0.0.1:2222"
+
+task:
+  - name: wait
+    script: sleep 5
+
+  - name: copy configuration
+    copy: {"src": "/local/remark42.yml", "dst": "/srv/remark42.yml", "mkdir": true}
+
+  - name: some local command
+    options: {local: true}
+    script: |
+      ls -la /srv
+      du -hcs /srv
+
+  - name: git
+    before: "echo before git"
+    after: "echo after git"
+    onerror: "echo onerror git"
+    script: |
+      git clone https://example.com/remark42.git /srv || true # clone if doesn't exists, but don't fail if exists
+      cd /srv
+      git pull
+
+  - name: docker
+    options: {no_auto: true}
+    script: |
+      docker pull umputun/remark42:latest
+      docker stop remark42 || true
+      docker rm remark42 || true
+      docker run -d --name remark42 -p 8080:8080 umputun/remark42:latest
+    env:
+      FOO: bar
+      BAR: qux