etcd: add systemd unit support for clustering

Refer https://etcd.io/docs/v3.5/op-guide/clustering/
for etcd clustering design background details.

etcd-new.service triggers only, when the config file available
in the specified path. This generic serive helps to start etcd
cluster based on the project specific use cases and config
files.

etcd-new.service only required to run on initial setup or new node
add into the existing cluster. All other use cases use regular
etcd.service to start etcd with existing cluster configuration.

Signed-off-by: ojayanth <ojayanth@in.ibm.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-extended/etcd/etcd/etcd-new.path

@@ -0,0 +1,9 @@
+[Unit]
+Description=Monitor the etcd config file changes
+
+[Path]
+PathChanged=/run/etcd-new.conf
+Unit=etcd-new.service
+
+[Install]
+WantedBy=multi-user.target

meta-oe/recipes-extended/etcd/etcd/etcd-new.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=etcd cluster member start/add service
+Documentation=https://etcd.io/docs/v3.5/op-guide/clustering/
+ConditionPathExists=!/var/lib/etcd/member
+ConditionPathExists=/run/etcd-new.conf
+OnFailure=etcd.service
+
+[Service]
+Type=notify
+EnvironmentFile=/run/etcd-new.conf
+ExecStart=/usr/bin/etcd
+Restart=no
+
+[Install]
+WantedBy=multi-user.target

meta-oe/recipes-extended/etcd/etcd_3.5.7.bb

@@ -10,6 +10,8 @@ SRC_URI = " \
     file://0001-test_lib.sh-remove-gobin-requirement-during-build.patch;patchdir=src/${GO_IMPORT} \
     file://etcd.service \
     file://etcd-existing.conf \
+    file://etcd-new.service \
+    file://etcd-new.path \
 "
 
 SRCREV = "215b53cf3b48ee761f4c40908b3874b2e5e95e9f"
@@ -53,7 +55,7 @@ go_do_compile:prepend() {
 
 REQUIRED_DISTRO_FEATURES = "systemd"
 SYSTEMD_PACKAGES = "${PN}"
-SYSTEMD_SERVICE:${PN}:append = " etcd.service"
+SYSTEMD_SERVICE:${PN}:append = " etcd.service etcd-new.service etcd-new.path"
 
 do_install:append() {
     install -d ${D}${bindir}/
@@ -63,6 +65,8 @@ do_install:append() {
     install -m 0644 ${WORKDIR}/etcd-existing.conf -D -t ${D}${sysconfdir}/etcd.d
     install -d ${D}${systemd_system_unitdir}
     install -m 0644 ${WORKDIR}/etcd.service ${D}${systemd_system_unitdir}/
+    install -m 0644 ${WORKDIR}/etcd-new.service ${D}${systemd_system_unitdir}/
+    install -m 0644 ${WORKDIR}/etcd-new.path ${D}${systemd_system_unitdir}/
 }
 
 FILES:${PN}:append = " ${sysconfdir}/etcd.d/etcd-existing.conf"