Add etcd

_sidebar.md

@@ -12,6 +12,7 @@
     - [Kafka](categories/apps/kafka.md)
     - [MQTT](categories/apps/mqtt.md)
     - [Elasticsearch](categories/apps/elasticsearch.md)
+    - [etcd](categories/apps/etcd.md)
 - [Database](categories/database.md)
 - [Application](categories/application.md)
 - [Web Scraping](categories/web-scraping.md)

categories/apps/etcd.md

@@ -0,0 +1,23 @@
+# etcd
+
+etcd is a strongly consistent, distributed key-value store that provides a reliable way to store data that needs to be accessed by a distributed system or cluster of machines. It gracefully handles leader elections during network partitions and can tolerate machine failure, even in the leader node.
+
+##  Tips
+
+
+### Make the k8s embedded single etcd to be a cluster
+
+Unfortunately, there is no straightfoward way to change the existing embedded etcd to a cluster.
+But we can leverage etcd `make-mirror` command to replicate the existing etcd to a new cluster.
+The steps are:
+
+1. Follow the guide to setup a new etcd cluster
+2. Run the following command to replicate k8s emmbedded etcd data to the new cluster
+
+```
+sudo ETCDCTL_API=3 etcdctl make-mirror https://new_etcd_node:2379 --endpoints=https://192.168.1.2:2379  --cacert=/k8s_etcd/ca.crt   --cert=/k8s_etcd/server.crt   --key=/k8s_etcd/server.key   --dest-cacert=/new_etcd/ca.pem   --dest-cert=/new_etcd/etcd.pem   --dest-key=/new_etcd/etcd-key.pem
+```
+3. On one of the new cluster node, to verify the data
+```
+sudo ETCDCTL_API=3 etcdctl get --prefix=true "" -w json  --endpoints=https://127.0.0.1:2379   --cacert=/new_etcd/ca.pem   --cert=/new_etcd/etcd.pem   --key=/new_etcd/etcd-key.pem
+```