Merge branch 'develop' into main

.github/workflows/AlmaLinux.yml

@@ -0,0 +1,61 @@
+# See: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
+
+# Workflow name
+name: AlmaLinux 8.5 RPM build
+
+# Run on event push
+on: push
+
+jobs:
+
+  #
+  # Build on AlmaLinux 8.5 using go-toolset
+  #
+  AlmaLinux-RPM-build:
+    runs-on: ubuntu-latest
+    # See: https://hub.docker.com/_/almalinux
+    container: almalinux:8.5
+    steps:
+
+    # Use dnf to install development packages
+    - name: Install development packages
+      run: dnf --assumeyes group install "Development Tools" "RPM Development Tools"
+
+    # Checkout git repository and submodules
+    # fetch-depth must be 0 to use git describe
+    # See: https://github.com/marketplace/actions/checkout
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        submodules: recursive
+        fetch-depth: 0
+
+    # Use dnf to install build dependencies
+    - name: Install build dependencies
+      run: dnf --assumeyes builddep scripts/cc-metric-collector.spec
+
+    - name: RPM build MetricCollector
+      id: rpmbuild
+      run: make RPM
+
+    # See: https://github.com/actions/upload-artifact
+    - name: Save RPM as artifact
+      uses: actions/upload-artifact@v2
+      with:
+        name: cc-metric-collector RPM for AlmaLinux 8.5
+        path: ${{ steps.rpmbuild.outputs.RPM }}
+    - name: Save SRPM as artifact
+      uses: actions/upload-artifact@v2
+      with:
+        name: cc-metric-collector SRPM for AlmaLinux 8.5
+        path: ${{ steps.rpmbuild.outputs.SRPM }}
+
+    # See: https://github.com/softprops/action-gh-release
+    - name: Release
+      uses: softprops/action-gh-release@v1
+      if: startsWith(github.ref, 'refs/tags/')
+      with:
+        name: cc-metric-collector-${{github.ref_name}}
+        files: |
+         ${{ steps.rpmbuild.outputs.RPM }}
+         ${{ steps.rpmbuild.outputs.SRPM }}

.github/workflows/RedHatUniversalBaseImage.yml

@@ -0,0 +1,61 @@
+# See: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
+
+# Workflow name
+name: Red Hat Universal Base Image 8 RPM build
+
+# Run on event push
+on: push
+
+jobs:
+
+  #
+  # Build on UBI 8 using go-toolset
+  #
+  UBI-8-RPM-build:
+    runs-on: ubuntu-latest
+    # See: https://catalog.redhat.com/software/containers/ubi8/ubi/5c359854d70cc534b3a3784e?container-tabs=gti
+    container: registry.access.redhat.com/ubi8/ubi:8.5-226.1645809065
+    steps:
+
+    # Use dnf to install development packages
+    - name: Install development packages
+      run: dnf --assumeyes --disableplugin=subscription-manager install rpm-build go-srpm-macros rpm-build-libs rpm-libs gcc make python38 git
+
+    # Checkout git repository and submodules
+    # fetch-depth must be 0 to use git describe
+    # See: https://github.com/marketplace/actions/checkout
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        submodules: recursive
+        fetch-depth: 0
+
+    # Use dnf to install build dependencies
+    - name: Install build dependencies
+      run: dnf --assumeyes --disableplugin=subscription-manager builddep scripts/cc-metric-collector.spec
+
+    - name: RPM build MetricCollector
+      id: rpmbuild
+      run: make RPM
+
+    # See: https://github.com/actions/upload-artifact
+    - name: Save RPM as artifact
+      uses: actions/upload-artifact@v2
+      with:
+        name: cc-metric-collector RPM for UBI 8
+        path: ${{ steps.rpmbuild.outputs.RPM }}
+    - name: Save SRPM as artifact
+      uses: actions/upload-artifact@v2
+      with:
+        name: cc-metric-collector SRPM for UBI 8
+        path: ${{ steps.rpmbuild.outputs.SRPM }}
+
+    # See: https://github.com/softprops/action-gh-release
+    - name: Release
+      uses: softprops/action-gh-release@v1
+      if: startsWith(github.ref, 'refs/tags/')
+      with:
+        name: cc-metric-collector-${{github.ref_name}}
+        files: |
+         ${{ steps.rpmbuild.outputs.RPM }}
+         ${{ steps.rpmbuild.outputs.SRPM }}

.github/workflows/rpmbuild.yml

@@ -1,58 +0,0 @@
-name: Run RPM Build
-on:
- push:
-  tags:
-  - '**'
-
-jobs:
-  build-alma-8_5:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-    - uses: TomTheBear/rpmbuild@alma8.5
-      id: rpm
-      name: Build RPM package on AlmaLinux 8.5
-      with:
-        spec_file: "./scripts/cc-metric-collector.spec"
-    - name: Save RPM as artifact
-      uses: actions/upload-artifact@v1.0.0
-      with:
-        name: cc-metric-collector RPM AlmaLinux 8.5
-        path: ${{ steps.rpm.outputs.rpm_path }}
-    - name: Save SRPM as artifact
-      uses: actions/upload-artifact@v1.0.0
-      with:
-        name: cc-metric-collector SRPM AlmaLinux 8.5
-        path: ${{ steps.rpm.outputs.source_rpm_path }}
-    - name: Release
-      uses: softprops/action-gh-release@v1
-      with:
-        name: cc-metric-collector-${{github.ref_name}}
-        files: |
-         ${{ steps.rpm.outputs.source_rpm_path }}
-         ${{ steps.rpm.outputs.rpm_path }}
-  build-rhel-ubi8:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-    - uses: TomTheBear/rpmbuild@rh-ubi8
-      id: rpm
-      name: Build RPM package on Red Hat Universal Base Image 8
-      with:
-        spec_file: "./scripts/cc-metric-collector.spec"
-    - name: Save RPM as artifact
-      uses: actions/upload-artifact@v1.0.0
-      with:
-        name: cc-metric-collector RPM Red Hat Universal Base Image 8
-        path: ${{ steps.rpm.outputs.rpm_path }}
-    - name: Save SRPM as artifact
-      uses: actions/upload-artifact@v1.0.0
-      with:
-        name: cc-metric-collector SRPM Red Hat Universal Base Image 8
-        path: ${{ steps.rpm.outputs.source_rpm_path }}
-    - name: Release
-      uses: softprops/action-gh-release@v1
-      with:
-        files: |
-         ${{ steps.rpm.outputs.source_rpm_path }}
-         ${{ steps.rpm.outputs.rpm_path }}

.github/workflows/runonce.yml

@@ -1,46 +1,68 @@
+# See: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
+
+# Workflow name
 name: Run Test
+
+# Run on event push
 on: push
 
 jobs:
+  #
+  # Job build-1-17
+  # Build on latest Ubuntu using golang version 1.17 
+  #
   build-1-17:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    # See: https://github.com/marketplace/actions/checkout
+    # Checkout git repository and submodules
+    - name: Checkout
+      uses: actions/checkout@v2
       with:
         submodules: recursive
 
     # See: https://github.com/marketplace/actions/setup-go-environment
     - name: Setup Golang
-      uses: actions/setup-go@v2.1.5
+      uses: actions/setup-go@v2
       with:
-        go-version: '^1.17.6'
+        go-version: '^1.17.7'
 
+    # Install libganglia
     - name: Setup Ganglia
       run: sudo apt install ganglia-monitor libganglia1
 
     - name: Build MetricCollector
       run: make
 
-    - name: Run MetricCollector
+    - name: Run MetricCollector once
       run: ./cc-metric-collector --once --config .github/ci-config.json
+
+  #
+  # Job build-1-16
+  # Build on latest Ubuntu using golang version 1.16
+  #
   build-1-16:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    # See: https://github.com/marketplace/actions/checkout
+    # Checkout git repository and submodules
+    - name: Checkout
+      uses: actions/checkout@v2
       with:
         submodules: recursive
 
     # See: https://github.com/marketplace/actions/setup-go-environment
     - name: Setup Golang
-      uses: actions/setup-go@v2.1.5
+      uses: actions/setup-go@v2
       with:
         go-version: '^1.16.7' # The version AlmaLinux 8.5 uses
 
+    # Install libganglia
     - name: Setup Ganglia
       run: sudo apt install ganglia-monitor libganglia1
 
     - name: Build MetricCollector
       run: make
 
-    - name: Run MetricCollectorlibganglia1
+    - name: Run MetricCollector once
       run: ./cc-metric-collector --once --config .github/ci-config.json

Makefile

@@ -56,3 +56,33 @@ vet:
 staticcheck:
 	go install honnef.co/go/tools/cmd/staticcheck@latest
 	$$(go env GOPATH)/bin/staticcheck ./...
+
+.ONESHELL:
+.PHONY: RPM
+RPM: scripts/cc-metric-collector.spec
+	@WORKSPACE="$${PWD}"
+	@SPECFILE="$${WORKSPACE}/scripts/cc-metric-collector.spec"
+	# Setup RPM build tree
+	@eval $$(rpm --eval "ARCH='%{_arch}' RPMDIR='%{_rpmdir}' SOURCEDIR='%{_sourcedir}' SPECDIR='%{_specdir}' SRPMDIR='%{_srcrpmdir}' BUILDDIR='%{_builddir}'")
+	@mkdir --parents --verbose "$${RPMDIR}" "$${SOURCEDIR}" "$${SPECDIR}" "$${SRPMDIR}" "$${BUILDDIR}"
+	# Create source tarball
+	@COMMITISH="HEAD"
+	@VERS=$$(git describe --tags $${COMMITISH})
+	@VERS=$${VERS#v}
+	@VERS=$${VERS//-/_}
+	@eval $$(rpmspec --query --queryformat "NAME='%{name}' VERSION='%{version}' RELEASE='%{release}' NVR='%{NVR}' NVRA='%{NVRA}'" --define="VERS $${VERS}" "$${SPECFILE}")
+	@PREFIX="$${NAME}-$${VERSION}"
+	@FORMAT="tar.gz"
+	@SRCFILE="$${SOURCEDIR}/$${PREFIX}.$${FORMAT}"
+	@git archive --verbose --format "$${FORMAT}" --prefix="$${PREFIX}/" --output="$${SRCFILE}" $${COMMITISH}
+	# Build RPM and SRPM
+	@rpmbuild -ba --define="VERS $${VERS}" --rmsource --clean "$${SPECFILE}"
+	# Report RPMs and SRPMs when in GitHub Workflow
+	@if [[ "$${GITHUB_ACTIONS}" == true ]]; then
+	@     RPMFILE="$${RPMDIR}/$${ARCH}/$${NVRA}.rpm"
+	@     SRPMFILE="$${SRPMDIR}/$${NVR}.src.rpm"
+	@     echo "RPM: $${RPMFILE}"
+	@     echo "SRPM: $${SRPMFILE}"
+	@     echo "::set-output name=SRPM::$${SRPMFILE}"
+	@     echo "::set-output name=RPM::$${RPMFILE}"
+	@fi

collectors/Makefile

@@ -55,16 +55,13 @@ $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION): $(BUILD_FOLDER)/likwid-$(LIKWID_VERSIO
 	tar -C $(BUILD_FOLDER) -xf $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION).tar.gz
 
 $(INSTALL_FOLDER)/liblikwid.a: $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION) $(INSTALL_FOLDER)
-	sed -i -e s+"PREFIX ?= .*"+"PREFIX = $(LIKWID_BASE)"+g \
-		-e s+"SHARED_LIBRARY = .*"+"SHARED_LIBRARY = false"+g \
-		-e s+"ACCESSMODE = .*"+"ACCESSMODE = $(ACCESSMODE)"+g \
-		-e s+"INSTALLED_ACCESSDAEMON = .*"+"INSTALLED_ACCESSDAEMON = $(DAEMON_INSTALLDIR)/likwid-accessD"+g \
-		$(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/config.mk
-	cd $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION) && make
-	cp $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/liblikwid.a $(INSTALL_FOLDER)
-	cp $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/ext/hwloc/liblikwid-hwloc.a $(INSTALL_FOLDER)
-	cp $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/src/includes/likwid*.h $(INSTALL_FOLDER)
-	cp $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/src/includes/bstrlib.h $(INSTALL_FOLDER)
+	cd "$(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)" && make "PREFIX=$(LIKWID_BASE)" "SHARED_LIBRARY=false" "ACCESSMODE=$(ACCESSMODE)" "INSTALLED_ACCESSDAEMON=$(DAEMON_INSTALLDIR)/likwid-accessD"
+	cp \
+	    $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/liblikwid.a \
+	    $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/ext/hwloc/liblikwid-hwloc.a \
+	    $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/src/includes/likwid*.h \
+	    $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/src/includes/bstrlib.h \
+	    $(INSTALL_FOLDER)
 
 $(DAEMON_INSTALLDIR)/likwid-accessD: $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/likwid-accessD
 	sudo -u $(DAEMON_USER) -g $(DAEMON_GROUP) install -m 4775 $(BUILD_FOLDER)/likwid-$(LIKWID_VERSION)/likwid-accessD $(DAEMON_INSTALLDIR)/likwid-accessD

collectors/metricCollector.go

@@ -13,29 +13,30 @@ import (
 )
 
 type MetricCollector interface {
-	Name() string
-	Init(config json.RawMessage) error
-	Initialized() bool
-	Read(duration time.Duration, output chan lp.CCMetric)
-	Close()
+	Name() string                                         // Name of the metric collector
+	Init(config json.RawMessage) error                    // Initialize metric collector
+	Initialized() bool                                    // Is metric collector initialized?
+	Read(duration time.Duration, output chan lp.CCMetric) // Read metrics from metric collector
+	Close()                                               // Close / finish metric collector
 }
 
 type metricCollector struct {
-	name string
-	init bool
-	meta map[string]string
+	name string            // name of the metric
+	init bool              // is metric collector initialized?
+	meta map[string]string // static meta data tags
 }
 
-// Name() returns the name of the metric collector
+// Name returns the name of the metric collector
 func (c *metricCollector) Name() string {
 	return c.name
 }
 
+// Setup is for future use
 func (c *metricCollector) setup() error {
 	return nil
 }
 
-// Initialized() indicates whether the metric collector has been initialized.
+// Initialized indicates whether the metric collector has been initialized
 func (c *metricCollector) Initialized() bool {
 	return c.init
 }
@@ -64,6 +65,7 @@ func stringArrayContains(array []string, str string) (int, bool) {
 	return -1, false
 }
 
+// SocketList returns the list of physical sockets as read from /proc/cpuinfo
 func SocketList() []int {
 	buffer, err := ioutil.ReadFile("/proc/cpuinfo")
 	if err != nil {
@@ -89,6 +91,7 @@ func SocketList() []int {
 	return packs
 }
 
+// CpuList returns the list of physical CPUs (in contrast to logical CPUs) as read from /proc/cpuinfo
 func CpuList() []int {
 	buffer, err := ioutil.ReadFile("/proc/cpuinfo")
 	if err != nil {
@@ -117,8 +120,8 @@ func CpuList() []int {
 // RemoveFromStringList removes the string r from the array of strings s
 // If r is not contained in the array an error is returned
 func RemoveFromStringList(s []string, r string) ([]string, error) {
-	for i, item := range s {
-		if r == item {
+	for i := range s {
+		if r == s[i] {
 			return append(s[:i], s[i+1:]...), nil
 		}
 	}

collectors/sampleMetric.go

@@ -22,6 +22,13 @@ type SampleCollector struct {
 	tags   map[string]string          // default tags
 }
 
+// Functions to implement MetricCollector interface
+// Init(...), Read(...), Close()
+// See: metricCollector.go
+
+// Init initializes the sample collector
+// Called once by the collector manager
+// All tags, meta data tags and metrics that do not change over the runtime should be set here
 func (m *SampleCollector) Init(config json.RawMessage) error {
 	var err error = nil
 	// Always set the name early in Init() to use it in cclog.Component* functions
@@ -56,12 +63,14 @@ func (m *SampleCollector) Init(config json.RawMessage) error {
 	return err
 }
 
+// Read collects all metrics belonging to the sample collector
+// and sends them through the output channel to the collector manager
 func (m *SampleCollector) Read(interval time.Duration, output chan lp.CCMetric) {
 	// Create a sample metric
 	timestamp := time.Now()
 
 	value := 1.0
-	// If you want to measure something for a specific amout of time, use interval
+	// If you want to measure something for a specific amount of time, use interval
 	// start := readState()
 	// time.Sleep(interval)
 	// stop := readState()
@@ -75,6 +84,8 @@ func (m *SampleCollector) Read(interval time.Duration, output chan lp.CCMetric)
 
 }
 
+// Close metric collector: close network connection, close files, close libraries, ...
+// Called once by the collector manager
 func (m *SampleCollector) Close() {
 	// Unset flag
 	m.init = false

receivers/README.md

@@ -9,32 +9,20 @@ The configuration file for the receivers is a list of configurations. The `type`
 ```json
 {
   "myreceivername" : {
+    "type": "receiver-type",
     <receiver-specific configuration>
   }
 }
 ```
 
-## Type `nats`
+This allows to specify
 
-```json
-{
-  "type": "nats",
-  "address": "<nats-URI or hostname>",
-  "port" : "<portnumber>",
-  "subject": "<subscribe topic>"
-}
-```
+## Available receivers
 
-The `nats` receiver subscribes to the topic `database` and listens on `address` and `port` for metrics in the InfluxDB line protocol.
+- [`nats`](./natsReceiver.md): Receive metrics from the NATS network
+- [`prometheus`](./prometheusReceiver.md): Scrape data from a Prometheus client
 
 # Contributing own receivers
 A receiver contains a few functions and is derived from the type `Receiver` (in `metricReceiver.go`):
-* `Start() error`
-* `Close()`
-* `Name() string`
-* `SetSink(sink chan lp.CCMetric)`
-* `New<Typename>(name string, config json.RawMessage)`
 
-The data structures should be set up in `Init()` like opening a file or server connection. The `Start()` function should either start a go routine or issue some other asynchronous mechanism for receiving metrics. The `Close()` function should tear down anything created in `Init()`.
-
-Finally, the receiver needs to be registered in the `receiveManager.go`. There is a list of receivers called `AvailableReceivers` which is a map (`receiver_type_string` -> `pointer to NewReceiver function`). Add a new entry with a descriptive name and the new receiver.
+For an example, check the [sample receiver](./sampleReceiver.go)

receivers/metricReceiver.go

@@ -8,6 +8,7 @@ type defaultReceiverConfig struct {
 	Type string `json:"type"`
 }
 
+// Receiver configuration: Listen address, port
 type ReceiverConfig struct {
 	Addr         string `json:"address"`
 	Port         string `json:"port"`
@@ -23,15 +24,17 @@ type receiver struct {
 
 type Receiver interface {
 	Start()
-	Close()
-	Name() string
-	SetSink(sink chan lp.CCMetric)
+	Close()                        // Close / finish metric receiver
+	Name() string                  // Name of the metric receiver
+	SetSink(sink chan lp.CCMetric) // Set sink channel
 }
 
+// Name returns the name of the metric receiver
 func (r *receiver) Name() string {
 	return r.name
 }
 
+// SetSink set the sink channel
 func (r *receiver) SetSink(sink chan lp.CCMetric) {
 	r.sink = sink
 }

receivers/natsReceiver.md

@@ -0,0 +1,21 @@
+## `nats` receiver
+
+The `nats` receiver can be used receive metrics from the NATS network. The `nats` receiver subscribes to the topic `database` and listens on `address` and `port` for metrics in the InfluxDB line protocol.
+
+### Configuration structure
+
+```json
+{
+  "<name>": {
+    "type": "nats",
+    "address" : "nats-server.example.org",
+    "port" : "4222",
+    "subject" : "subject"
+  }
+}
+```
+
+- `type`: makes the receiver a `nats` receiver
+- `address`: Address of the NATS control server
+- `port`: Port of the NATS control server
+- `subject`: Subscribes to this subject and receive metrics

receivers/prometheusReceiver.md

@@ -10,7 +10,7 @@ The `prometheus` receiver can be used to scrape the metrics of a single `prometh
     "type": "prometheus",
     "address" : "testpromhost",
     "port" : "12345",
-    "port" : "/prometheus",
+    "path" : "/prometheus",
     "interval": "5s",
     "ssl" : true,
   }

receivers/sampleReceiver.go

@@ -7,6 +7,7 @@ import (
 	cclog "github.com/ClusterCockpit/cc-metric-collector/internal/ccLogger"
 )
 
+// SampleReceiver configuration: receiver type, listen address, port
 type SampleReceiverConfig struct {
 	Type string `json:"type"`
 	Addr string `json:"address"`
@@ -24,6 +25,10 @@ type SampleReceiver struct {
 	// wg   sync.WaitGroup
 }
 
+// Implement functions required for Receiver interface
+// Start(), Close()
+// See: metricReceiver.go
+
 func (r *SampleReceiver) Start() {
 	cclog.ComponentDebug(r.name, "START")
 
@@ -44,6 +49,7 @@ func (r *SampleReceiver) Start() {
 	// }()
 }
 
+// Close receiver: close network connection, close files, close libraries, ...
 func (r *SampleReceiver) Close() {
 	cclog.ComponentDebug(r.name, "CLOSE")
 
@@ -54,13 +60,21 @@ func (r *SampleReceiver) Close() {
 	// r.wg.Wait()
 }
 
+// New function to create a new instance of the receiver
+// Initialize the receiver by giving it a name and reading in the config JSON
 func NewSampleReceiver(name string, config json.RawMessage) (Receiver, error) {
 	r := new(SampleReceiver)
-	r.name = fmt.Sprintf("HttpReceiver(%s)", name)
+
+	// Set name of SampleReceiver
+	// The name should be chosen in such a way that different instances of SampleReceiver can be distinguished
+	r.name = fmt.Sprintf("SampleReceiver(%s)", name)
 
 	// Set static information
 	r.meta = map[string]string{"source": r.name}
 
+	// Set defaults in r.config
+	// Allow overwriting these defaults by reading config JSON
+
 	// Read the sample receiver specific JSON config
 	if len(config) > 0 {
 		err := json.Unmarshal(config, &r.config)

scripts/cc-metric-collector.spec

@@ -1,5 +1,5 @@
 Name:           cc-metric-collector
-Version:        0.2
+Version:        %{VERS}
 Release:        1%{?dist}
 Summary:        Metric collection daemon from the ClusterCockpit suite
 

sinks/metricSink.go

@@ -10,17 +10,18 @@ type defaultSinkConfig struct {
 }
 
 type sink struct {
-	meta_as_tags bool
-	name         string
+	meta_as_tags bool   // Use meta data tags as tags
+	name         string // Name of the sink
 }
 
 type Sink interface {
-	Write(point lp.CCMetric) error
-	Flush() error
-	Close()
-	Name() string
+	Write(point lp.CCMetric) error // Write metric to the sink
+	Flush() error                  // Flush buffered metrics
+	Close()                        // Close / finish metric sink
+	Name() string                  // Name of the metric sink
 }
 
+// Name returns the name of the metric sink
 func (s *sink) Name() string {
 	return s.name
 }

sinks/sampleSink.go

@@ -10,15 +10,22 @@ import (
 )
 
 type SampleSinkConfig struct {
-	defaultSinkConfig // defines JSON tags for 'type' and 'meta_as_tags'
-	// Add additional options
+	// defines JSON tags for 'type' and 'meta_as_tags'
+	// See: metricSink.go
+	defaultSinkConfig
+	// Additional config options, for SampleSink
 }
 
 type SampleSink struct {
-	sink                    // declarate 'name' and 'meta_as_tags'
+	// declares elements 	'name' and 'meta_as_tags'
+	sink
 	config SampleSinkConfig // entry point to the SampleSinkConfig
 }
 
+// Implement functions required for Sink interface
+// Write(...), Flush(), Close()
+// See: metricSink.go
+
 // Code to submit a single CCMetric to the sink
 func (s *SampleSink) Write(point lp.CCMetric) error {
 	log.Print(point)
@@ -39,9 +46,13 @@ func (s *SampleSink) Close() {
 // Initialize the sink by giving it a name and reading in the config JSON
 func NewSampleSink(name string, config json.RawMessage) (Sink, error) {
 	s := new(SampleSink)
+
+	// Set name of sampleSink
+	// The name should be chosen in such a way that different instances of SampleSink can be distinguished
 	s.name = fmt.Sprintf("SampleSink(%s)", name) // Always specify a name here
 
 	// Set defaults in s.config
+	// Allow overwriting these defaults by reading config JSON
 
 	// Read in the config JSON
 	if len(config) > 0 {
@@ -52,7 +63,7 @@ func NewSampleSink(name string, config json.RawMessage) (Sink, error) {
 	}
 
 	// Check if all required fields in the config are set
-	// Use 'len(s.config.Option) > 0' for string settings
+	// E.g. use 'len(s.config.Option) > 0' for string settings
 
 	// Establish connection to the server, library, ...
 	// Check required files exist and lookup path(s) of executable(s)