feat: add LiteFS example for Flipt in the examples directory (#2297)

* feat: add LiteFS example for Flipt in the examples directory

* chore: add details section

* chore: add newline to end of README file

* chore: make changes to address comments on exposing ports

examples/database/litefs/Dockerfile

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+FROM alpine
+
+COPY --from=flyio/litefs:0.5 /usr/local/bin/litefs /usr/local/bin/litefs
+COPY --from=flipt/flipt:latest /flipt /usr/local/bin/flipt
+
+RUN mkdir -p /etc/flipt/config && \
+    mkdir -p /var/opt/flipt
+
+COPY --from=flipt/flipt:latest /etc/flipt/config/default.yml /etc/flipt/config/default.yml
+RUN chown -R root:root /var/opt/flipt /etc/flipt
+
+ADD litefs.yml /etc/litefs.yml
+
+RUN apk add bash fuse3 sqlite ca-certificates
+
+ENTRYPOINT litefs mount

examples/database/litefs/README.md

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+# LiteFS
+
+LiteFS is a distributed file system that replicates SQLite databases to other nodes at the file system level. It works by using [FUSE](https://www.kernel.org/doc/html/next/filesystems/fuse.html) to detect writes to the file system and determines how and if those should be replicated.
+
+This example will demonstrate how to run Flipt over LiteFS.
+
+## Requirements
+
+- [Docker](https://www.docker.com/)
+- [docker-compose](https://docs.docker.com/compose/install/)
+
+## Running the Example
+
+1. Run `docker-compose up` from this directory
+1. Open the Flipt UI (default: [http://localhost:8080](http://localhost:8080))
+
+## Details
+
+`docker compose` will spin up two instances of Flipt with embedded SQLite databases. On top of these instances is an nginx proxy that will forward "write" requests, anything but `GET`, to the primary. `GET` requests will be served from the instance's embedded SQLite database.
+
+LiteFS describes a few [caveats](https://fly.io/docs/litefs/proxy/#how-it-works) that must be kept in mind.
+
+## Data
+
+You can view the data on any one of the instances located at [primary](http://localhost:8081) or the [replica](http://localhost:8082), but remember that writes will only happen on the primary or the nginx proxy, the replica instance will not be able to accpet writes.

examples/database/litefs/docker-compose.yml

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+version: '3'
+services:
+  nginx:
+    build: ./nginx
+    ports:
+      - "8080:80"
+  primary:
+    build: .
+    privileged: true
+    ports:
+      - "8081:8080"
+    environment:
+      IS_PRIMARY: "true"
+  replica:
+    build: .
+    ports:
+      - "8082:8080"
+    restart: on-failure
+    privileged: true
+    environment:
+      IS_PRIMARY: "false"

examples/database/litefs/litefs.yml

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+log:
+  debug: true
+
+fuse:
+  dir: "/var/opt/flipt"
+
+data:
+  dir: "/var/lib/litefs"
+
+lease:
+  type: "static"
+
+  advertise-url: "http://primary:20202"
+
+  candidate: $IS_PRIMARY
+
+exec:
+  - cmd: "flipt"

examples/database/litefs/nginx/Dockerfile

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+FROM nginx:alpine
+
+COPY ./nginx.conf /etc/nginx/nginx.conf
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]

examples/database/litefs/nginx/nginx.conf

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+http {
+    upstream primary {
+        server primary:8080;
+    }
+    upstream all {
+        server primary:8080;
+        server replica:8080;
+    }
+    server {
+        listen 80;
+        location / {
+            # Basically all writes should go to this primary,
+            # while reads go to everything else.
+            if ($request_method ~ "(PUT|POST|PATCH|DELETE)") {
+                proxy_pass http://primary;
+            }
+            proxy_pass http://all;
+        }
+    }
+}
+
+events { }