Support Litefs database migrations with multiple machines in primary

See https://community.fly.io/t/litefs-database-migrations-with-multiple-machines-in-primary-how-to-determine-writeable-primary-machine/18752/7?u=rubys

lib/generators/templates/Dockerfile.erb

@@ -286,7 +286,11 @@ ENV <%= deploy_env.join(" \\\n ") %>
 <% else -%>
 # Entrypoint sets up the container.
 <% end -%>
+<% if using_litefs? -%>
+ENTRYPOINT ["litefs", "mount"]
+<% else -%>
 ENTRYPOINT ["/rails/bin/docker-entrypoint"]
+<% end -%>
 
 <% if procfile.size > 1 -%>
 # Build a Procfile for production use
@@ -307,7 +311,7 @@ VOLUME /data
 CMD ["foreman", "start", "--procfile=<%= options.procfile %>"]
 <% elsif procfile.size > 1 -%>
 CMD ["foreman", "start", "--procfile=Procfile.prod"]
-<% else -%>
+<% elsif !using_litefs? -%>
 CMD <%= procfile.values.first.split(" ").inspect %>
 <% end -%>
 <% end -%>

lib/generators/templates/litefs.yml.erb

@@ -77,6 +77,8 @@ proxy:
 # "static" which assigns a single node to be the primary and does
 # not failover.
 lease:
+ promote: true
+
  # Required. Must be either "consul" or "static".
  type: "consul"
 
@@ -114,3 +116,19 @@ lease:
  # can become leader. This buffer is intended to prevent
  # overlap in leadership due to clock skew or in-flight calls.
  lock-delay: "1s"
+
+exec:
+ # Only run migrations on candidate nodes.
+ - cmd: "./bin/rails db:prepare"
+ if-candidate: true
+
+ # Then run the application server on all nodes.
+<% if !options.procfile.blank? -%>
+ - cmd: "foreman start --procfile=<%= options.procfile %>"
+<% elsif procfile.size > 1 -%>
+ - cmd: "foreman start --procfile=Procfile.prod"
+<% elsif !using_litefs? -%>
+ - cmd: <%= procfile.values.first.split(" ").inspect %>
+<% else -%>
+ - cmd: "./bin/rails server"
+<% end -%> 

test/results/litefs/Dockerfile

@@ -73,9 +73,8 @@ ENV DATABASE_URL="sqlite3:///litefs/production.sqlite3" \
  PORT="3001"
 
 # Entrypoint prepares the database.
-ENTRYPOINT ["/rails/bin/docker-entrypoint"]
+ENTRYPOINT ["litefs", "mount"]
 
 # Start the server by default, this can be overwritten at runtime
 EXPOSE 3000
 VOLUME /data
-CMD ["./bin/rails", "server"]

test/results/litefs/config/litefs.yml

@@ -77,6 +77,8 @@ proxy:
 # "static" which assigns a single node to be the primary and does
 # not failover.
 lease:
+ promote: true
+
  # Required. Must be either "consul" or "static".
  type: "consul"
 
@@ -114,3 +116,12 @@ lease:
  # can become leader. This buffer is intended to prevent
  # overlap in leadership due to clock skew or in-flight calls.
  lock-delay: "1s"
+
+exec:
+ # Only run migrations on candidate nodes.
+ - cmd: "./bin/rails db:prepare"
+ if-candidate: true
+
+ # Then run the application server on all nodes.
+ - cmd: "./bin/rails server"
+