Docker Redis container - Command option

Question

I'm trying to create a Redis container in Docker and run a command to initialize the data structures. But I can't even get a simple command like redis-cli SET counter "4" to work.

But even with a command like redis-cli --help, it doesn't work. It seems that after any command, it exists with the line:

sockets_server_redis_1 exited with code 1

When I use either of the following lines:

command: "redis-cli SET counter "4" && redis-cli GET counter"
command: sh -c "redis-cli SET counter "4" && redis-cli GET counter"

the complete output I get is:

Attaching to sockets_server_redis_1
redis_1 | Could not connect to Redis at 127.0.0.1:6379: Connection refused
sockets_server_redis_1 exited with code 1

This is my docker-compose.yml file:

version: "3.8"

services:
  redis:
    image: redis
    command: "redis-cli SET counter "4" && redis-cli GET counter"
    ports:
      - 6379:6379

However, if I run this command in the CLI through Docker, it works.

So, I have two questions:

1. Why do the set and get commands not work but redis-cli --help works?

2. Why does the process exit after the initial command, and how can I initialize the data structures and not have it exit?

question from:https://stackoverflow.com/questions/65650046/docker-redis-container-command-option

Answer 1

The command instruction in a Docker Compose file maps to the CMD directive in a Dockerfile, which is the one and only command that the container will execute upon launching (the command can always be overridden when you launch the container, which is what docker-compose is doing under the hood when you set that option).

For a Redis container, whose purpose is to bring up a Redis server, the command should always be the command that actually launches the server. When you override it to instead run redis-cli commands, the server does not come up, so the client can't connect and you see the errors you're getting. The --help option for redis-cli doesn't open a connection, which is why it doesn't error (to answer your question #1).

For question #2, see above as to why the process is exiting after the command runs. To actually solve your problem, there are a range of options, but I would suggest a second container which just runs a script that a) waits until Redis is reachable and b) initializes the data structures once it is. A utility like wait-for-it can make step A easier, though you might be able to get away with just Compose's default depends_on functionality (it doesn't wait for the actual service to be ready, just the container, but Redis comes up very quickly):

version: "3.8"

services:
  redis:
    image: redis
    ports:
      - 6379:6379

  redis_init:
    image: redis # we need an image with redis-cli available, so might as well re-use it
    command: "redis-cli -h redis SET counter "4""
    depends_on:
      - redis

From testing locally, this works, though I can't say how reliable it might be on every system.