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/container/container.go

@@ -90,6 +90,17 @@ func (c Container) Enabled() (bool, bool) {
 	return parsedBool, true
 }
 
+// Scope returns the value of the scope UID label and if the label
+// was set.
+func (c Container) Scope() (string, bool) {
+	rawString, ok := c.getLabelValue(scope)
+	if !ok {
+		return "", false
+	}
+
+	return rawString, true
+}
+
 // Links returns a list containing the names of all the containers to which
 // this container is linked.
 func (c Container) Links() []string {

pkg/container/metadata.go

@@ -6,6 +6,7 @@ const (
 	enableLabel           = "com.centurylinklabs.watchtower.enable"
 	dependsOnLabel        = "com.centurylinklabs.watchtower.depends-on"
 	zodiacLabel           = "com.centurylinklabs.zodiac.original-image"
+	scope                 = "com.centurylinklabs.watchtower.scope"
 	preCheckLabel         = "com.centurylinklabs.watchtower.lifecycle.pre-check"
 	postCheckLabel        = "com.centurylinklabs.watchtower.lifecycle.post-check"
 	preUpdateLabel        = "com.centurylinklabs.watchtower.lifecycle.pre-update"

pkg/container/mocks/FilterableContainer.go

@@ -55,3 +55,27 @@ func (_m *FilterableContainer) Name() string {
 
 	return r0
 }
+
+// Scope provides a mock function with given fields:
+func (_m *FilterableContainer) Scope() (string, bool) {
+	ret := _m.Called()
+
+	var r0 string
+
+	if rf, ok := ret.Get(0).(func() string); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(string)
+	}
+
+	var r1 bool
+
+	if rf, ok := ret.Get(1).(func() bool); ok {
+		r1 = rf()
+	} else {
+		r1 = ret.Get(1).(bool)
+	}
+
+	return r0, r1
+}
+

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)

pkg/types/filterable_container.go

@@ -6,4 +6,5 @@ type FilterableContainer interface {
 	Name() string
 	IsWatchtower() bool
 	Enabled() (bool, bool)
+	Scope() (string, bool)
 }