Documentation: add systemd, Container Linux guide

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

Documentation/docs.md

@@ -42,6 +42,7 @@ Administrators who need to create reliable and scalable key-value stores for the
 
  - [Supported systems][supported_platforms]
  - [Docker container][container_docker]
+ - [Container Linux, systemd][container_linux_platform]
  - [rkt container][container_rkt]
  - [Amazon Web Services][aws_platform]
  - [FreeBSD][freebsd_platform]
@@ -101,6 +102,7 @@ Answers to [common questions] about etcd.
 [understand_apis]: learning/api.md
 [versioning]: op-guide/versioning.md
 [supported_platforms]: op-guide/supported-platform.md
+[container_linux_platform]: platforms/container-linux-systemd.md
 [freebsd_platform]: platforms/freebsd.md
 [aws_platform]: platforms/aws.md
 [experimental]: dev-guide/experimental_apis.md

Documentation/platforms/container-linux-systemd.md

@@ -0,0 +1,203 @@
+# Run etcd on Container Linux with systemd
+
+The following guide shows how to run etcd with [systemd][systemd-docs] under [Container Linux][container-linux-docs].
+
+## Provisioning an etcd cluster
+
+Cluster bootstrapping in Container Linux is simplest with [Ignition][container-linux-ignition]; `coreos-metadata.service` dynamically fetches the machine's IP for discovery. Note that etcd's discovery service protocol is only meant for bootstrapping, and cannot be used with runtime reconfiguration or cluster monitoring.
+
+The [Container Linux Config Transpiler][container-linux-ct] compiles etcd configuration files into Ignition configuration files:
+
+```yaml container-linux-config:norender
+etcd:
+  version: 3.2.0
+  name: s1
+  data_dir: /var/lib/etcd
+  advertise_client_urls:       http://{PUBLIC_IPV4}:2379
+  initial_advertise_peer_urls: http://{PRIVATE_IPV4}:2380
+  listen_client_urls:          http://0.0.0.0:2379
+  listen_peer_urls:            http://{PRIVATE_IPV4}:2380
+  discovery:                   https://discovery.etcd.io/<token>
+```
+
+`ct` would produce the following Ignition Config:
+
+```
+$ ct --platform=gce --in-file /tmp/ct-etcd.cnf
+{"ignition":{"version":"2.0.0","config"...
+```
+
+```json ignition-config
+{
+  "ignition":{"version":"2.0.0","config":{}},
+  "storage":{},
+  "systemd":{
+    "units":[{
+      "name":"etcd-member.service",
+      "enable":true,
+      "dropins":[{
+        "name":"20-clct-etcd-member.conf",
+        "contents":"[Unit]\nRequires=coreos-metadata.service\nAfter=coreos-metadata.service\n\n[Service]\nEnvironmentFile=/run/metadata/coreos\nEnvironment=\"ETCD_IMAGE_TAG=v3.1.8\"\nExecStart=\nExecStart=/usr/lib/coreos/etcd-wrapper $ETCD_OPTS \\\n  --name=\"s1\" \\\n  --data-dir=\"/var/lib/etcd\" \\\n  --listen-peer-urls=\"http://${COREOS_GCE_IP_LOCAL_0}:2380\" \\\n  --listen-client-urls=\"http://0.0.0.0:2379\" \\\n  --initial-advertise-peer-urls=\"http://${COREOS_GCE_IP_LOCAL_0}:2380\" \\\n  --advertise-client-urls=\"http://${COREOS_GCE_IP_EXTERNAL_0}:2379\" \\\n  --discovery=\"https://discovery.etcd.io/\u003ctoken\u003e\""}]}]},
+      "networkd":{},
+      "passwd":{}}
+```
+
+To avoid accidental misconfiguration, the transpiler helpfully verifies etcd configurations when generating Ignition files:
+
+```yaml container-linux-config:norender
+etcd:
+  version: 3.2.0
+  name: s1
+  data_dir_x: /var/lib/etcd
+  advertise_client_urls:       http://{PUBLIC_IPV4}:2379
+  initial_advertise_peer_urls: http://{PRIVATE_IPV4}:2380
+  listen_client_urls:          http://0.0.0.0:2379
+  listen_peer_urls:            http://{PRIVATE_IPV4}:2380
+  discovery:                   https://discovery.etcd.io/<token>
+```
+
+```
+$ ct --platform=gce --in-file /tmp/ct-etcd.cnf
+warning at line 3, column 2
+Config has unrecognized key: data_dir_x
+```
+
+See [Container Linux Provisioning][container-linux-provision] for more details.
+
+## etcd 3.x service
+
+[Container Linux][container-linux-docs] does not include etcd 3.x binaries by default. Different versions of etcd 3.x can be fetched via `etcd-member.service`.
+
+Confirm unit file exists:
+
+```
+systemctl cat etcd-member.service
+```
+
+Check if the etcd service is running:
+
+```
+systemctl status etcd-member.service
+```
+
+Example systemd drop-in unit to override the default service settings:
+
+```bash
+cat > /tmp/20-cl-etcd-member.conf <<EOF
+[Service]
+Environment="ETCD_IMAGE_TAG=v3.2.0"
+Environment="ETCD_DATA_DIR=/var/lib/etcd"
+Environment="ETCD_SSL_DIR=/etc/ssl/certs"
+Environment="ETCD_OPTS=--name s1 \
+  --listen-client-urls https://10.240.0.1:2379 \
+  --advertise-client-urls https://10.240.0.1:2379 \
+  --listen-peer-urls https://10.240.0.1:2380 \
+  --initial-advertise-peer-urls https://10.240.0.1:2380 \
+  --initial-cluster s1=https://10.240.0.1:2380,s2=https://10.240.0.2:2380,s3=https://10.240.0.3:2380 \
+  --initial-cluster-token mytoken \
+  --initial-cluster-state new \
+  --client-cert-auth \
+  --trusted-ca-file /etc/ssl/certs/etcd-root-ca.pem \
+  --cert-file /etc/ssl/certs/s1.pem \
+  --key-file /etc/ssl/certs/s1-key.pem \
+  --peer-client-cert-auth \
+  --peer-trusted-ca-file /etc/ssl/certs/etcd-root-ca.pem \
+  --peer-cert-file /etc/ssl/certs/s1.pem \
+  --peer-key-file /etc/ssl/certs/s1-key.pem \
+  --auto-compaction-retention 1"
+EOF
+mv /tmp/20-cl-etcd-member.conf /etc/systemd/system/etcd-member.service.d/20-cl-etcd-member.conf
+```
+
+Or use a Container Linux Config:
+
+```yaml container-linux-config:norender
+systemd:
+  units:
+    - name: etcd-member.service
+      dropins:
+        - name: conf1.conf
+          contents: |
+            [Service]
+            Environment="ETCD_SSL_DIR=/etc/ssl/certs"
+
+etcd:
+  version: 3.2.0
+  name: s1
+  data_dir: /var/lib/etcd
+  listen_client_urls:          https://0.0.0.0:2379
+  advertise_client_urls:       https://{PUBLIC_IPV4}:2379
+  listen_peer_urls:            https://{PRIVATE_IPV4}:2380
+  initial_advertise_peer_urls: https://{PRIVATE_IPV4}:2380
+  initial_cluster:             s1=https://{PRIVATE_IPV4}:2380,s2=https://10.240.0.2:2380,s3=https://10.240.0.3:2380
+  initial_cluster_token:       mytoken
+  initial_cluster_state:       new
+  client_cert_auth:            true
+  trusted_ca_file:             /etc/ssl/certs/etcd-root-ca.pem
+  cert-file:                   /etc/ssl/certs/s1.pem
+  key-file:                    /etc/ssl/certs/s1-key.pem
+  peer-client-cert-auth:       true
+  peer-trusted-ca-file:        /etc/ssl/certs/etcd-root-ca.pem
+  peer-cert-file:              /etc/ssl/certs/s1.pem
+  peer-key-file:               /etc/ssl/certs/s1-key.pem
+  auto-compaction-retention:   1
+```
+
+```
+$ ct --platform=gce --in-file /tmp/ct-etcd.cnf
+{"ignition":{"version":"2.0.0","config"...
+```
+
+To see all runtime drop-in changes for system units:
+
+```
+systemd-delta --type=extended
+```
+
+To enable and start:
+
+```
+systemctl daemon-reload
+systemctl enable --now etcd-member.service
+```
+
+To see the logs:
+
+```
+journalctl --unit etcd-member.service --lines 10
+```
+
+To stop and disable the service:
+
+```
+systemctl disable --now etcd-member.service
+```
+
+## etcd 2.x service
+
+[Container Linux][container-linux-docs] includes a unit file `etcd2.service` for etcd 2.x, which will be removed in the near future. See [Container Linux FAQ][container-linux-faq] for more details.
+
+Confirm unit file is installed:
+
+```
+systemctl cat etcd2.service
+```
+
+Check if the etcd service is running:
+
+```
+systemctl status etcd2.service
+```
+
+To stop and disable:
+
+```
+systemctl disable --now etcd2.service
+```
+
+[systemd-docs]: https://github.com/systemd/systemd
+[container-linux-docs]: https://coreos.com/os/docs/latest
+[container-linux-faq]: https://github.com/coreos/docs/blob/master/etcd/os-faq.md
+[container-linux-provision]: https://github.com/coreos/docs/blob/master/os/provisioning.md
+[container-linux-ignition]: https://github.com/coreos/docs/blob/master/ignition/what-is-ignition.md
+[container-linux-ct]: https://github.com/coreos/container-linux-config-transpiler