Heng Li blog

Running rail app in docker

2019-06-12T00:00:00+00:00

Step 1:

First, using `Dockfile` to Define the project

we need to create Dockefile, you can cop sample dockerfile from offical websie (This is sample Dockerfile copy from docker offical website)

FROM ruby:2.5
RUN apt-get update -qq && apt-get install -y nodejs postgresql-client
RUN mkdir /myapp
WORKDIR /myapp
COPY Gemfile /myapp/Gemfile
COPY Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

# Add a script to be executed every time the container starts.
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]
EXPOSE 3000

# Start the main process.
CMD ["rails", "server", "-b", "0.0.0.0"]

second, create a Gemfile to just load rails.

source 'https://rubygems.org'
gem 'rails', '~>5' # specify rails version in here

Third, create an empty `Gemfile.lock` To build `Dockefile`

touch Gemfile.lock

Fourth, create shell script, named `entrypoint.sh`

The purpose of entrypoint scipt is to fix a Rails-specific issue that prevents the server from restarting when a certain server.pid file pre-exists.

#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails.
rm -f /myapp/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile).
exec "$@"

Finaly,`create docker-compose.yml` file

version: '3'
services:
  db:
    image: mysql
    volumes:
      - ./tmp/db:/var/lib/mysql/data
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/myapp
    ports:
      - "3000:3000"
    depends_on:
      - db

Step 2: Build the project

Now it’s time to generate the rails skelton app using docker compose run command:

docker-compose run web rails new . --force --no-deps --database=postgresql

If you ever modify gem file. which you’ll do. you need run:

docker-compose build

Step 3: Connect the database

This is tricky part. when I followed docker website. I was stuck in this step. the offical mysql docker image which is somehow can’t initial. I got

[ERROR] --initialize specified but the data directory has files in it. Aborting.

After google for a while. I found a solution which is change db image source in docker-compose.yml file

from image: mysql to image: mariadb the detail discuss about this issue is here

Now we can boot the app with docker-compose up:

docker-compose up Finally, you need to create the database. In another terminal, run: docker-compose run web rake db:create

Flutter network connection issues

2019-05-14T00:00:00+00:00

Flutter network connection issues(faild host lookup)

I tried to call api from emulator to my host machine and I got following error message E/flutter (16241): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: SocketException: Failed host lookup: 'us1.uszcn.local' (OS Error: No address associated with hostname, errno = 7) It took me one hour to figure out what’s the issues is.

Step 1: Check whether internet pemisson was granted

Open your AdroidManifest.xml file check whether internet pemisson was granted. if not add following to the file ` `

If after edit AdroidManifest.xml not solve your issue. which didb’t solve my issue. please process to step 2:

Step2: Check your emulator proxy setting.

According to the offical document. you need to set hostname as 10.0.2.2: port number is whichever you using in your local machine.

Try again, if you can call you service. or in your emulator,open a webbrowser visit 10.0.2.2:portname(the port you’re using in your local machine). if you can visit, that means your proxy setting is working.

if you still can’t error messge. look up your host file in your local machine. you may setting up custom domain for it

step3:Edit your emulator host file.

open a terminal and change your directory to /Library/Android/sdk/ default image is read only. so you have to change it to writeble. under sdk directory change to tools directory type command ` ./emulator -avd huawei_T3_10_API_24 -writable-systemthis will enable you copy your local host file to emulator. open another terminal. under /Library/Android/sdk/platorm_tools directory,type command:./adb root && ./adb -s emulator-5554 remount && ./adb -s push /etc/hosts /system/etc/hosts` if your don't what your device_name is. type './adb devices' in your terminal. You would see all your devices. This command will copy your local machine host file to emulator.

now, you can check whether it successfully push to your emulator. type ./adb shell in your terminal, it will lunch a shell. type cat etc/host you will see your host from your emulator.

References:

Ruby symbol vs string!

2019-05-10T00:00:00+00:00

Ruby has this unique datatype called symbol. it’s very simlar to string. but there is one important difference it is immutable. The second thing is it share its memory with other symbol if they have same name. for Example: if you define :username. later you define again this symbol :username. it’s the same object id ,which means it share the same memory with the symbol we defined early.