Add step-by-step instructions for setting up Postgres using Block Storage

postgres/README.md

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+# PostgreSQL Setup
+
+The purpose of this guide is to show how _we_ setup Postgres on a standard VPS.
+No prior **DevOps** experience is assumed/expected,
+however some understanding of basic Postgres concepts is _useful_.
+
+> **Note**: if you are new to Postgres or need a refresher,
+please see: 
+[github.com/dwyl/**learn-postgresql**](https://github.com/dwyl/learn-postgresql)
+
+
+## 1. Create a VPS Instance
+
+If you don't already have a Virtual Private Server (VPS) instance,
+create one. 
+
+> In the case of this guide, 
+we are using DigitalOcean 
+because they have a good balance of Price/Performance.
+> We did a bunch of research into the comparative cost/perf:
+[learn-devops/issues/58](https://github.com/dwyl/learn-devops/issues/58#issuecomment-660650080)
+We concluded that the **NVMe SSD Block Storage** of DigitalOcean,
+was the best in the cost/perf tradeoff. 
+
+At the time of writing,
+there is no 1-click Postgres setup in the DO Marketplace:
+https://marketplace.digitalocean.com
+So we are doing our setup from scratch.
+
+
+Visit: 
+Select the instance Operating System and Plan:
+![do-create-01-select-instance-type](https://user-images.githubusercontent.com/194400/87891845-4a7bed80-ca33-11ea-8bf5-eb3095eeafe6.png)
+
+
+
+Select the instance Operating System and Plan:
+![do-create-01-select-instance-type](https://user-images.githubusercontent.com/194400/87891845-4a7bed80-ca33-11ea-8bf5-eb3095eeafe6.png)
+
+Scroll down to the "Add Block Storage" section and enter 1gb into the field:
+![do-create-02-block-storage](https://user-images.githubusercontent.com/194400/87891890-667f8f00-ca33-11ea-9043-cca1b44cc334.png)
+
+We're going to increase the size in a later step, so keep it low for now just to set it up.
+https://www.digitalocean.com/docs/volumes/how-to/increase-size/
+
+Select `Ext4` for the filesystem and then select the datacenter region that bests suits your needs.
+
+> We selected `Ext4` filesystem based on reading this post:
+https://blog.pgaddict.com/posts/postgresql-performance-on-ext4-and-xfs
+It _appears_ to be 10% faster for Postgres. 
+
+Scroll down until you see the "Choose a hostname" field. Enter a relevant name, in our case "hits":
+![do-create-04-hostname](https://user-images.githubusercontent.com/194400/87892697-b3646500-ca35-11ea-854a-364a4ae0a964.png)
+
+Scroll to the bottom of the page and click "**Create Droplet**".
+
+Given that the data directory will be on the _separate_ block storage,
+we aren't bothering with the $1/month backup.
+
+Once your server has been created,
+follow the initial server setup guide:
+https://www.digitalocean.com/community/tutorials/initial-server-setup-with-ubuntu-18-04
+
+
+
+
+2. Install Postgres
+
+Following this guide:
+https://www.digitalocean.com/community/tutorials/how-to-install-and-use-postgresql-on-ubuntu-18-04
+
+Login to the VPS using ssh:
+```
+ssh [email protected]
+```
+
+Update the OS and install Postgres:
+
+```sh
+sudo apt update
+sudo apt install postgresql postgresql-contrib
+```
+
+Once everything is installed,
+Switch to the Postgres user:
+
+```
+sudo -i -u postgres
+```
+
+You should see the following in your terminal 
+to indicate that you're logged in as the postgres user:
+
+```
+postgres@hits:~$
+```
+
+
+```
+createuser --interactive
+```
+
+```
+hitsnodelete
+```
+This username is fairly self-evident.
+We want a user that can `insert` records but not `delete` any data.
+
+```
+Shall the new role be a superuser? (y/n)
+```
+
+Select `n`, for all options
+as we don't _want_ our user to be a `superuser`.
+
+
+## 3. Change Postgres Directory to use Block Storage
+
+
+Following this guide:
+https://www.digitalocean.com/community/tutorials/how-to-move-a-postgresql-data-directory-to-a-new-location-on-ubuntu-18-04
+
+
+Login to postgres:
+```
+sudo -u postgres psql
+```
+
+Display the data directory:
+```
+SHOW data_directory;
+```
+
+You should see:
+```
+       data_directory
+-----------------------------
+ /var/lib/postgresql/10/main
+(1 row)
+```
+
+Quit postgres:
+
+```
+\q
+```
+
+Shut down postgres:
+
+```
+sudo systemctl stop postgresql
+```
+
+Confirm the status of postgres:
+```
+sudo systemctl status postgresql
+```
+
+You should see something similar to the following:
+```
+● postgresql.service - PostgreSQL RDBMS
+   Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
+   Active: inactive (dead) since Mon 2020-07-20 03:11:02 UTC; 7s ago
+ Main PID: 8928 (code=exited, status=0/SUCCESS)
+
+Jul 20 02:25:23 hits systemd[1]: Starting PostgreSQL RDBMS...
+Jul 20 02:25:23 hits systemd[1]: Started PostgreSQL RDBMS.
+Jul 20 03:11:02 hits systemd[1]: Stopped PostgreSQL RDBMS.
+```
+
+
+Copy the postgres data directory to the block storage volume:
+
+```
+sudo rsync -av /var/lib/postgresql /mnt/volume_lon1_01
+```
+
+In our case our mounted block storage is `/mnt/volume_lon1_01`
+
+
+Rename `main` data to `main.bak` just so we have a backup:
+```
+sudo mv /var/lib/postgresql/10/main /var/lib/postgresql/10/main.bak
+```
+
+
+Edit the postgres config:
+
+```
+sudo nano /etc/postgresql/10/main/postgresql.conf
+```
+
+
+Find the `data_directory` line and update it to:
+```
+data_directory = '/mnt/volume_lon1_01/postgresql/10/main'
+```
+
+Save and quit the file.
+
+Start postgres again:
+
+```
+sudo systemctl start postgresql
+```
+
+Check the status:
+```
+sudo systemctl status postgresql
+```
+
+You should see the following:
+
+```
+● postgresql.service - PostgreSQL RDBMS
+   Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
+   Active: active (exited) since Mon 2020-07-20 03:17:59 UTC; 5s ago
+  Process: 20422 ExecStart=/bin/true (code=exited, status=0/SUCCESS)
+ Main PID: 20422 (code=exited, status=0/SUCCESS)
+
+Jul 20 03:17:59 hits systemd[1]: Starting PostgreSQL RDBMS...
+Jul 20 03:17:59 hits systemd[1]: Started PostgreSQL RDBMS.
+```
+
+Login to `psql`:
+
+```
+sudo -u postgres psql
+```
+
+Show the `data_directory`:
+
+```
+SHOW data_directory;
+```
+
+You should see:
+
+```
+             data_directory
+----------------------------------------
+ /mnt/volume_lon1_01/postgresql/10/main
+(1 row)
+```
+
+Success.