Today I was researching and trying docker, and with the most of things I was impressed. There are still some questions for me about docker.
Can anyone more experienced than me with Docker tell me what is the best way to login to postgres container (run bash), in order to view some postgres configuration files, view postgres logs, log into postgres shell, execute pg_dump for example, etc. etc..., and everything this while postgres process is running.
I see that people usually run one process per container, and with this approach I am not sure what is the best way to do mentioned actions on container which runs postgres?
Any advices?
Thanks!
You can usually get a shell like this:
docker exec -it some-node bash
The canonical docker way would be not to log in to the running db container, but instead do docker logs or link other containers to do maintenance tasks (e.g. docker run -it --rm --link <my-pg-container>:pg <my-pg-image> pgsql --host pg etc..
Related
I'm trying to docker-containerize PostgreSQL server and this container will have many other applications as well. The need is that, PostgreSQL server data should be mapped to the host volume so that when container is stopped, we won't lose the data. Also that, the next time when we start the container, the same directory can be mapped again and postgres can use the old data. Below is the DOCKERFILE. Note that I'm using ubuntu 22.04 on the host.
FROM ubuntu:22.04
ENV DEBIAN_FRONTEND noninteractive
RUN apt install -y postgresql
ENTRYPOINT ["tail", "-f", "/dev/null"]
Docker image is built using the command
docker build -t pg_test .
and the container is run using the command
docker run --name test -v /home/me/data:/var/lib/postgresql/14/main pg_test
'/home/me/data' is the host directory which is empty where I want to map the postgres server data. '/var/lib/postgresql/14/main' is the directory inside the docker container where the postgres is supposed to store the data.
Once the docker container starts, I enter the docker container using the command
docker exec -it test bash
and once I'm inside, I'm trying to start the PostgreSQL service. But PostgreSQL fails to start as there is no data in '/var/lib/postgresql/14/main' directory. I understand that since I have mapped an empty host directory to '/var/lib/postgresql/14/main' directory, postgres doesn't have the files required to start.
I understand that I'm doing it the wrong way, but I couldn't find a way around it. Can anyone please help me to do this the right way, if there is one?
Any help would be appreciable.
You should use the postgres docker image, it will set up the db for you when you start the container, you can find instructions on https://hub.docker.com/_/postgres
If you must use a custom image, you will need to initialize the db yourself, usually by running initdb or whatever your system provides.
But really you should use the appropriate docker image, and if you need more services you start them in their own container and connect them to the postgres one
I'm very new to using docker and I've created a postgres container using
docker run --name mytrainingdb -e POSTGRES_PASSWORD=mysecretpassword -d postgres. Then I connected to it with docker exec -it <container-id> bash and then psql.
Then I stop the container.
My query is, what do I do reconnect to the same database? I tried to run same docker run command, but it says the name 'mytrainingdb' is used, which means it is trying to create it afresh, which is not what I want. Hope my expectation is right, as in when I restart my laptop or resume work I can just restart the same container and my data/config would be preserved?
The documentation also mentions that we can link a host directory to volume of pg container to have the stored data accessible to us, but I'm ok with docker managing my storage for that database.
You will have error when you try to re-run the same command, because docker is trying to create a new container with same name as the previous one "mytrainingdb". If you close docker and reopen it you will still find your container , but its not running , you can start it again with docker start mytrainingdb or you can remove it with docker rm mytrainingdb .
However , dont restart docker because you want to create a new container with the same name! If you want to start a new container with the same name and your container is still running you can first stop it with docker stop mytrainingdb and docker rm mytrainingdb or you can just do docker rm -f mytrainingdb (this will remove you running container with force ) and then create a new container..
As for the volumes ,you just created one by default which is named is kind of hash , and its found at volumes/var/lib/docker/volumes/ .Because generally containers such PostgreSQL, or databases in general persists volumes. The volume gets created when running the container and is handy to save persistent data, whether you start the container with -v or not.
The volume you talked about in your question , is called mounted volume , is when you basically just bind a certain directory or file from the host (outside) to inside the container
docker run -v /hostdir:/containerdir in your case docker run -v /hostdir:/var/lib/postgresql/data
If you restart docker or your computer running containers won't be automatically restarted. You can start your container again with docker start mytrainingdb (related question), then connect with your docker exec command.
(one tip: instead of running bash, then psql, you can directly run psql, e.g. docker exec -it mytrainingdb psql --user postgres)
Your understanding of data persistence is correct, docker will manage the data and it will still be around.
From the postgres image documentation
There are several ways to store data used by applications that run in Docker containers. We encourage users of the postgres images to familiarize themselves with the options available, including:
Let Docker manage the storage of your database data by writing the database files to disk on the host system using its own internal volume management. This is the default and is easy and fairly transparent to the user. The downside is that the files may be hard to locate for tools and applications that run directly on the host system, i.e. outside containers.
You can add --rm argument so that whenever you stop the container manually, or container stops for any reasons (his task is done or it fails), it will remove that container.
In your case, you can use this:
docker run --name mytrainingdb --rm -e POSTGRES_PASSWORD=mysecretpassword -d postgres
So, I pulled the postgres image down from docker. I followed a tutorial which explained what's going with the command below and the the whole docker pull. I can log in to the instance fine. But when I restart my computer or shutdown docker I end up goign through similar setup steps and am not able to access the postgres instance anymore. Can someone explain what's going on here:
Run this command
docker run --rm --name pg-docker -e POSTGRES_PASSWORD=docker -d postgres -p 5432:5432 -v $HOME/docker/volumes/postgres:/var/lib/postgresql/data postgres
log in via PG admin.
Nothing, instance not available.
So, I feel like I am missing a step at one point I had executed a command like this:
docker exec -it c5b8bdd0820b35a01ea153a44e82458a6285cf484b701b2b2d6d4210266fb4f8 bash
which gave me acess to the shell for the image, after doing that I was able then to use PGAdmin, however, I feel like that may have been coincidence? As this does not work currently.
So, what am I doing wrong? What's an easier way to do this?
The --rm causes Docker to automatically remove the container when it exits. Remove it.
You can also add --restart always and your container will be up after restart.
I'm currently working with Docker, I use mongo image for my DB container. For persistent storage, I mounted host machine's directory(e.g. /var/docker/data/db) to container(e.g. /data/db).
By now, whenever I wanted to run mongo shell and connect to my db I was doing these things:
Attach to running MongoDB container using docker exec -it <container> bash
Run mongo shell inside the container
Do some job
But I think it'll be much better if I could run mongod separately on the host machine, not in the container, and then connect to it even when the container is not running.
So is it possible to doing so? If I run two mongod process on the same directory(files), will there be an file access conflict?
If someone did similar kind of work, share me your experience please. Thanks.
I want to make two minor improvements on the official MongoDB docker so that it starts with the --auth enabled and uses a separate data container to store the data. What's the best way to do this?
If all are set, how should I start the shell? Will it be possible for someone without a username and password to access any of the databases available? Which directory should I backup?
EDIT
Apparently, this is not enough:
docker run --name mymongoname1 -v /my/local/dir:/data/db -d -P mongo:latest
OK, so partial answer, because I haven't messed around with docker auth.
Containerising storage is done with a storage container. That's basically a container created off a token instance, with some volumes assigned.
So for elasticsearch (which I know isn't mongo, but it is at least a NoSQL db) I've been using:
docker create -v /es_data:/es_data --name elasticsearch_data es-base /bin/true
Then:
docker run -d -p 9200:9200 --vols-from elasticsearch_data elasticsearch-2.1.0
This connects the container volume to my es container - in this example it passes through a host volume, but you don't actually need to any more, because the container can hold the data in the docker filesystem. (And then I think you can push the data container around too, but I've not got that far!)
If you run ps -a you will see the data container in Created state. Just watch if you're doing a cleanup script that you don't delete it, because unlike running containers, you can freely delete it...