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‎docs/solutions/ha-etcd.md

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# Configure etcd distributed store
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The distributed configuration store provides a reliable way to store data that needs to be accessed by large scale distributed systems. The most popular implementation of the distributed configuration store is etcd. etcd is deployed as a cluster for fault-tolerance and requires an odd number of members (n/2+1) to agree on updates to the cluster state. An etcd cluster helps establish a consensus among nodes during a failover and manages the configuration for the three PostgreSQL instances.
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This document provides configuration for etcd version 3.5.x. For how to configure etcd cluster with earlier versions of etcd, read the blog post by _Fernando Laudares Camargos_ and _Jobin Augustine_ [PostgreSQL HA with Patroni: Your Turn to Test Failure Scenarios](https://www.percona.com/blog/postgresql-ha-with-patroni-your-turn-to-test-failure-scenarios/)
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If you [installed the software from tarballs](../tarball.md), check how you [enable etcd](../enable-extensions.md#etcd).
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The `etcd` cluster is first started in one node and then the subsequent nodes are added to the first node using the `add `command.
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!!! note
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Users with deeper understanding of how etcd works can configure and start all etcd nodes at a time and bootstrap the cluster using one of the following methods:
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* Static in the case when the IP addresses of the cluster nodes are known
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* Discovery service - for cases when the IP addresses of the cluster are not known ahead of time.
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See the [How to configure etcd nodes simultaneously](../how-to.md#how-to-configure-etcd-nodes-simultaneously) section for details.
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### Configure `node1`
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1. Create the configuration file. You can edit the sample configuration file `/etc/etcd/etcd.conf.yaml` or create your own one. Replace the node name and IP address with the actual name and IP address of your node.
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```yaml title="/etc/etcd/etcd.conf.yaml"
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name: 'node1'
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initial-cluster-token: PostgreSQL_HA_Cluster_1
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initial-cluster-state: new
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initial-cluster: node1=http://10.104.0.1:2380
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data-dir: /var/lib/etcd
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initial-advertise-peer-urls: http://10.104.0.1:2380
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listen-peer-urls: http://10.104.0.1:2380
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advertise-client-urls: http://10.104.0.1:2379
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listen-client-urls: http://10.104.0.1:2379
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```
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2. Start the `etcd` service to apply the changes on `node1`.
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```{.bash data-prompt="$"}
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$ sudo systemctl enable --now etcd
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$ sudo systemctl start etcd
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$ sudo systemctl status etcd
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```
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3. Check the etcd cluster members on `node1`:
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```{.bash data-prompt="$"}
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$ sudo etcdctl member list --write-out=table --endpoints=http://10.104.0.1:2379
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```
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Sample output:
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```{.text .no-copy}
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+------------------+---------+-------+----------------------------+----------------------------+------------+
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| ID | STATUS | NAME | PEER ADDRS | CLIENT ADDRS | IS LEARNER |
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+------------------+---------+-------+----------------------------+----------------------------+------------+
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| 9d2e318af9306c67 | started | node1 | http://10.104.0.1:2380 | http://10.104.0.1:2379 | false |
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+------------------+---------+-------+----------------------------+----------------------------+------------+
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```
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4. Add the `node2` to the cluster. Run the following command on `node1`:
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```{.bash data-prompt="$"}
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$ sudo etcdctl member add node2 --peer-ulrs=http://10.104.0.2:2380
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```
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??? example "Sample output"
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```{.text .no-copy}
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Added member named node2 with ID 10042578c504d052 to cluster
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etcd_NAME="node2"
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etcd_INITIAL_CLUSTER="node2=http://10.104.0.2:2380,node1=http://10.104.0.1:2380"
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etcd_INITIAL_CLUSTER_STATE="existing"
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```
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### Configure `node2`
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1. Create the configuration file. You can edit the sample configuration file `/etc/etcd/etcd.conf.yaml` or create your own one. Replace the node names and IP addresses with the actual names and IP addresses of your nodes.
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```yaml title="/etc/etcd/etcd.conf.yaml"
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name: 'node2'
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initial-cluster-token: PostgreSQL_HA_Cluster_1
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initial-cluster-state: existing
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initial-cluster: node1=http://10.104.0.1:2380,node2=http://10.104.0.2:2380
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data-dir: /var/lib/etcd
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initial-advertise-peer-urls: http://10.104.0.2:2380
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listen-peer-urls: http://10.104.0.2:2380
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advertise-client-urls: http://10.104.0.2:2379
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listen-client-urls: http://10.104.0.2:2379
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```
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3. Start the `etcd` service to apply the changes on `node2`:
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```{.bash data-prompt="$"}
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$ sudo systemctl enable --now etcd
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$ sudo systemctl start etcd
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$ sudo systemctl status etcd
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```
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### Configure `node3`
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1. Add `node3` to the cluster. **Run the following command on `node1`**
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```{.bash data-prompt="$"}
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$ sudo etcdctl member add node3 http://10.104.0.3:2380
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```
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2. On `node3`, create the configuration file. You can edit the sample configuration file `/etc/etcd/etcd.conf.yaml` or create your own one. Replace the node names and IP addresses with the actual names and IP addresses of your nodes.
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```yaml title="/etc/etcd/etcd.conf.yaml"
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name: 'node3'
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initial-cluster-token: PostgreSQL_HA_Cluster_1
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initial-cluster-state: existing
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initial-cluster: node1=http://10.104.0.1:2380,node2=http://10.104.0.2:2380,node3=http://10.104.0.3:2380
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data-dir: /var/lib/etcd
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initial-advertise-peer-urls: http://10.104.0.3:2380
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listen-peer-urls: http://10.104.0.3:2380
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advertise-client-urls: http://10.104.0.3:2379
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listen-client-urls: http://10.104.0.3:2379
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```
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3. Start the `etcd` service to apply the changes.
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```{.bash data-prompt="$"}
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$ sudo systemctl enable --now etcd
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$ sudo systemctl start etcd
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$ sudo systemctl status etcd
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```
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4. Check the etcd cluster members.
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```{.bash data-prompt="$"}
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$ sudo etcdctl member list
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```
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??? example "Sample output"
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```
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2d346bd3ae7f07c4: name=node2 peerURLs=http://10.104.0.2:2380 clientURLs=http://10.104.0.2:2379 isLeader=false
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8bacb519ebdee8db: name=node3 peerURLs=http://10.104.0.3:2380 clientURLs=http://10.104.0.3:2379 isLeader=false
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c5f52ea2ade25e1b: name=node1 peerURLs=http://10.104.0.1:2380 clientURLs=http://10.104.0.1:2379 isLeader=true
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```

‎docs/solutions/ha-init-setup.md

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# Initial setup for high availability
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This guide provides instructions on how to set up a highly available PostgreSQL cluster with Patroni. This guide relies on the provided [architecture](ha-architecture.md) for high-availability.
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## Preconditions
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1. This is an example deployment where etcd runs on the same host machines as the Patroni and PostgreSQL and there is a single dedicated HAProxy host. Alternatively etcd can run on different set of nodes.
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If etcd is deployed on the same host machine as Patroni and PostgreSQL, separate disk system for etcd and PostgreSQL is recommended due to performance reasons.
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2. For this setup, we will use the nodes that have the following IP addresses:
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| Node name | Public IP address | Internal IP address
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|---------------|-------------------|--------------------
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| node1 | 157.230.42.174 | 10.104.0.7
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| node2 | 68.183.177.183 | 10.104.0.2
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| node3 | 165.22.62.167 | 10.104.0.8
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| HAProxy-demo | 134.209.111.138 | 10.104.0.6
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!!! note
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We recommend not to expose the hosts/nodes where Patroni / etcd / PostgreSQL are running to public networks due to security risks. Use Firewalls, Virtual networks, subnets or the like to protect the database hosts from any kind of attack.
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## Initial setup
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It’s not necessary to have name resolution, but it makes the whole setup more readable and less error prone. Here, instead of configuring a DNS, we use a local name resolution by updating the file `/etc/hosts`. By resolving their hostnames to their IP addresses, we make the nodes aware of each other’s names and allow their seamless communication.
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1. Set the hostname for nodes. Run the following command on each node. Change the node name to `node1`, `node2` and `node3` respectively:
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```{.bash data-prompt="$"}
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$ sudo hostnamectl set-hostname node1
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```
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2. Modify the `/etc/hosts` file of each PostgreSQL node to include the hostnames and IP addresses of the remaining nodes. Add the following at the end of the `/etc/hosts` file on all nodes:
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=== "node1"
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```text hl_lines="3 4"
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# Cluster IP and names
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10.104.0.1 node1
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10.104.0.2 node2
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10.104.0.3 node3
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```
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=== "node2"
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```text hl_lines="2 4"
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# Cluster IP and names
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10.104.0.1 node1
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10.104.0.2 node2
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10.104.0.3 node3
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```
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=== "node3"
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```text hl_lines="2 3"
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# Cluster IP and names
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10.104.0.1 node1
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10.104.0.2 node2
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10.104.0.3 node3
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```
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=== "HAproxy-demo"
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The HAProxy instance should have the name resolution for all the three nodes in its `/etc/hosts` file. Add the following lines at the end of the file:
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```text hl_lines="4 5 6"
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# Cluster IP and names
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10.104.0.6 HAProxy-demo
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10.104.0.1 node1
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10.104.0.2 node2
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10.104.0.3 node3
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```
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‎docs/solutions/ha-install-software.md

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# Install the software
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## Install Percona Distribution for PostgreSQL
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Run the following commands as root or with `sudo` privileges.
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=== "On Debian / Ubuntu"
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1. Disable the upstream `postgresql-{{pgversion}}` package.
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2. Install the `percona-release` repository management tool
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--8<-- "percona-release-apt.md"
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3. Enable the repository
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```{.bash data-prompt="$"}
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$ sudo percona-release setup ppg{{pgversion}}
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```
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4. Install Percona Distribution for PostgreSQL package
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```{.bash data-prompt="$"}
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$ sudo apt install percona-postgresql-{{pgversion}}
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```
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=== "On RHEL and derivatives"
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1. Check the [platform specific notes](../yum.md#for-percona-distribution-for-postgresql-packages)
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2. Install the `percona-release` repository management tool
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--8<-- "percona-release-yum.md"
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3. 3. Enable the repository
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```{.bash data-prompt="$"}
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$ sudo percona-release setup ppg{{pgversion}}
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```
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4. Install Percona Distribution for PostgreSQL package
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```{.bash data-prompt="$"}
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$ sudo apt install percona-postgresql{{pgversion}}-server
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```
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!!! important
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**Don't** initialize the cluster and start the `postgresql` service. The cluster initialization and setup are handled by Patroni during the bootsrapping stage.
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## Install Patroni, etcd, pgBackRest
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=== "On Debian / Ubuntu"
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1. Install some Python and auxiliary packages to help with Patroni and etcd
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```{.bash data-prompt="$"}
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$ sudo apt install python3-pip python3-dev binutils
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```
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2. Install etcd, Patroni, pgBackRest packages:
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```{.bash data-prompt="$"}
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$ sudo apt install percona-patroni \
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etcd etcd-server etcd-client \
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percona-pgbackrest
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```
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3. Stop and disable all installed services:
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```{.bash data-prompt="$"}
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$ sudo systemctl stop {etcd,patroni,postgresql}
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$ sudo systemctl disable {etcd,patroni,postgresql}
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```
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4. Even though Patroni can use an existing Postgres installation, remove the data directory to force it to initialize a new Postgres cluster instance.
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```{.bash data-prompt="$"}
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$ sudo systemctl stop postgresql
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$ sudo rm -rf /var/lib/postgresql/{{pgversion}}/main
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```
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=== "On RHEL and derivatives"
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1. Install some Python and auxiliary packages to help with Patroni and etcd
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```{.bash data-prompt="$"}
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$ sudo yum install python3-pip python3-devel binutils
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```
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2. Install etcd, Patroni, pgBackRest packages. Check [platform specific notes for Patroni](../yum.md#for-percona-patroni-package):
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```{.bash data-prompt="$"}
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$ sudo yum install percona-patroni \
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etcd python3-python-etcd\
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percona-pgbackrest
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```
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3. Stop and disable all installed services:
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```{.bash data-prompt="$"}
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$ sudo systemctl stop {etcd,patroni,postgresql}
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$ systemctl disable {etcd,patroni,postgresql}
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```
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