instance refused connection. is your app listening on 0.0.0.0:3000? make sure it is not only listening on 127.0.0.1

[Pello]

I deployed my Rails application, but it’s not working due to the following error, resulting in an HTTP ERROR 502. Could you help me resolve this issue?

...
`instance refused connection. is your app listening on 0.0.0.0:3000? make sure it is not only listening on 127.0.0.1`
...

Below is the Dockerfile:

...
# Entrypoint prepares the database.
ENTRYPOINT ["/rails/bin/docker-entrypoint"]
# Start server via Thruster by default, this can be overwritten at runtime
EXPOSE 3000
CMD ["./bin/thrust", "./bin/rails", "server"]
...

This Dockerfile was automatically generated by the rails new command.
/rails/bin/docker-entrypoint is as follows:

#!/bin/bash -e

# Enable jemalloc for reduced memory usage and latency.
if [ -z "${LD_PRELOAD+x}" ]; then
    LD_PRELOAD=$(find /usr/lib -name libjemalloc.so.2 -print -quit)
    export LD_PRELOAD
fi

# If running the rails server then create or migrate existing database
if [ "${@: -2:1}" == "./bin/rails" ] && [ "${@: -1:1}" == "server" ]; then
  ./bin/rails db:prepare
fi

exec "${@}"

Below is the fly.toml file:

app = 'xxx'
primary_region = 'xxx'

[build]
dockerfile = 'Dockerfile'

[http_service]
internal_port = 3000
force_https = true
auto_stop_machines = 'stop'
auto_start_machines = true
min_machines_running = 1
processes = ['app']

[[vm]]
memory = '512mb'
cpu_kind = 'shared'
cpus = 1

---

I tried adding the following to fly.toml, but the error message did not change:

[env]
PORT = "3000"

I replaced the production CMD with the following command, which I use in the development Dockerfile, but the error message remained the same:

- CMD ["./bin/thrust", "./bin/rails", "server"]
+ CMD ["rails", "server", "-b", "0.0.0.0", "-p", "3000"]

I believe the application will work if I can change it to listen on 0.0.0.0:3000, but I’m not sure where to make this change.

[rubys]

What’s in your logs? You are trying the right things, but if your Rails application isn’t starting for other reasons, that would explain this error.

Existing Rails Apps

[Pello]

Thank you for reviewing my question and for sharing the documentation link.
By running fly logs, I was able to identify the error and resolve it, which ultimately fixed the HTTP ERROR 502 issue.

---

When I ran fly logs, the following error was displayed:

ActiveRecord::AdapterNotSpecified: The `cable` database is not configured for the `production` environment.

Since I wasn’t planning to use Action Cable, I had commented out the following cable section in the database.yml file:

production:
  primary: &primary_production
    <<: *default
    database: production
...
  # cable: 
  #   <<: *primary_production 
  #   database: production_cable 
  #   migrations_paths: db/cable_migrate

By uncommenting this section, I was able to resolve the HTTP ERROR 502 issue.

---

I had been checking the logs in the “Live Logs” section of the fly.io console, but the ActiveRecord::AdapterNotSpecified: error didn’t show up there, so I wasn’t able to notice it.