Redis – Create a single container instead of 3 different containers

First of all, running redis, postgres and your "main container" in one container is NOT best practice.
Typically you should have 3 separate containers (single app per container) communicating over the network. Sometimes we want to run two or more lightweight services inside the same container but redis and postgres aren’t such services.
I recommend reading: best practices for building containers.

However, it’s possible to have multiple services in the same docker container using the supervisord process management system.
I will run both redis and postgres services in one docker container (it’s similar to your issue) to illustrate you how it works. It’s for demonstration purposes only.

This is a directory structure, we only need Dockerfile and supervisor.conf (supervisord config file):

$ tree example_container/
example_container/
├── Dockerfile
└── supervisor.conf

First, I created a supervisord configuration file with redis and postgres services defined:

$ cat example_container/supervisor.conf
[supervisord]
nodaemon=true

[program:redis] 
command=redis-server # command to run redis service
autorestart=true
stderr_logfile=/dev/stdout
stderr_logfile_maxbytes = 0
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes = 0


[program:postgres]
command=/usr/lib/postgresql/12/bin/postgres -D /var/lib/postgresql/12/main/ -c config_file=/etc/postgresql/12/main/postgresql.conf # command to run postgres service
autostart=true
autorestart=true
stderr_logfile=/dev/stdout
stderr_logfile_maxbytes = 0
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes = 0
user=postgres
environment=HOME="/var/lib/postgresql",USER="postgres"

Next I created a simple Dockerfile:

$ cat example_container/Dockerfile
FROM ubuntu:latest
ARG DEBIAN_FRONTEND=noninteractive

# Installing redis and postgres
RUN apt-get update && apt-get install -y supervisor redis-server postgresql-12

# Copying supervisor configuration file to container
ADD supervisor.conf /etc/supervisor.conf

# Initializing redis and postgres services using supervisord
CMD ["supervisord","-c","/etc/supervisor.conf"]

And then I built the docker image:

$ docker build -t example_container:v1 .

Finally I ran and tested docker container using the image above:

$ docker run --name multi_services -dit example_container:v1
472c7b2eac7441360126f8fcd0cc80e0e63ac3039f8195715a3a400f6288a236


$ docker exec -it multi_services bash
root@472c7b2eac74:/# ps aux   
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root           1  0.7  0.1  27828 23372 pts/0    Ss+  10:04   0:00 /usr/bin/python3 /usr/bin/supervisord -c /etc/supervisor.conf
postgres       8  0.1  0.1 212968 28972 pts/0    S    10:04   0:00 /usr/lib/postgresql/12/bin/postgres -D /var/lib/postgresql/12/main/ -c config_file=/etc/postgresql/12/main/postgresql.conf
root           9  0.1  0.0  47224  6216 pts/0    Sl   10:04   0:00 redis-server *:6379
...

root@472c7b2eac74:/# netstat -tulpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:6379            0.0.0.0:*               LISTEN      9/redis-server *:6
tcp        0      0 127.0.0.1:5432          0.0.0.0:*               LISTEN      8/postgres
tcp6       0      0 :::6379                 :::*                    LISTEN      9/redis-server *:6

As you can see it is possible to have multiple services in a single container but this is a NOT recommended approach that should be used ONLY for testing.