Adds scopeUID config to enable multiple instances of Watchtower (#511)

* Adds scopeUID config to enable multiple instances of Watchtower

* Adds tests for multiple instance support with scopeuid

* Adds docs on scope monitoring and multiple instance support

* Adds multiple instances docs to mkdocs config file

* Changes multiple instances check and refactors naming for scope feature

* Applies linter suggestions

* Fixes documentation on Watchtower monitoring scope

pkg/filters/filters.go

@@ -51,8 +51,24 @@ func FilterByDisabledLabel(baseFilter t.Filter) t.Filter {
 	}
 }
 
+// FilterByScope returns all containers that belongs to a specific scope
+func FilterByScope(scope string, baseFilter t.Filter) t.Filter {
+	if scope == "" {
+		return baseFilter
+	}
+	
+	return func(c t.FilterableContainer) bool {
+		containerScope, ok := c.Scope()
+		if ok && containerScope == scope {
+			return baseFilter(c)
+		}
+
+		return false
+	}
+}
+
 // BuildFilter creates the needed filter of containers
-func BuildFilter(names []string, enableLabel bool) t.Filter {
+func BuildFilter(names []string, enableLabel bool, scope string) t.Filter {
 	filter := NoFilter
 	filter = FilterByNames(names, filter)
 	if enableLabel {
@@ -60,6 +76,11 @@ func BuildFilter(names []string, enableLabel bool) t.Filter {
 		// if the label is specifically set.
 		filter = FilterByEnableLabel(filter)
 	}
+	if scope != "" {
+		// If a scope has been defined, containers should only be considered
+		// if the scope is specifically set.
+		filter = FilterByScope(scope, filter)
+	}
 	filter = FilterByDisabledLabel(filter)
 	return filter
 }

pkg/filters/filters_test.go

@@ -67,6 +67,29 @@ func TestFilterByEnableLabel(t *testing.T) {
 	container.AssertExpectations(t)
 }
 
+func TestFilterByScope(t *testing.T) {
+	var scope string
+	scope = "testscope"
+
+	filter := FilterByScope(scope, NoFilter)
+	assert.NotNil(t, filter)
+
+	container := new(mocks.FilterableContainer)
+	container.On("Scope").Return("testscope", true)
+	assert.True(t, filter(container))
+	container.AssertExpectations(t)
+
+	container = new(mocks.FilterableContainer)
+	container.On("Scope").Return("nottestscope", true)
+	assert.False(t, filter(container))
+	container.AssertExpectations(t)
+
+	container = new(mocks.FilterableContainer)
+	container.On("Scope").Return("", false)
+	assert.False(t, filter(container))
+	container.AssertExpectations(t)
+}
+
 func TestFilterByDisabledLabel(t *testing.T) {
 	filter := FilterByDisabledLabel(NoFilter)
 	assert.NotNil(t, filter)
@@ -91,7 +114,7 @@ func TestBuildFilter(t *testing.T) {
 	var names []string
 	names = append(names, "test")
 
-	filter := BuildFilter(names, false)
+	filter := BuildFilter(names, false, "")
 
 	container := new(mocks.FilterableContainer)
 	container.On("Name").Return("Invalid")
@@ -127,7 +150,7 @@ func TestBuildFilterEnableLabel(t *testing.T) {
 	var names []string
 	names = append(names, "test")
 
-	filter := BuildFilter(names, true)
+	filter := BuildFilter(names, true, "")
 
 	container := new(mocks.FilterableContainer)
 	container.On("Enabled").Return(false, false)