How to customize the configuration file of the off

Question

I'm using the official Postgres Docker image trying to customize its configuration. For this purpose, I use the command sed to change max_connections for example:

sed -i -e"s/^max_connections = 100.*$/max_connections = 1000/" /var/lib/postgresql/data/postgresql.conf

I tried two methods to apply this configuration. The first is by adding the commands to a script and copying it within the init folder "/docker-entrypoint-initdb.d". The second method is by running them directly within my Dockerfile with "RUN" command (this method worked fine with a non-official Postgresql image with a different path to the configuration file "/etc/postgres/..."). In both cases the changes fail because the configuration file is missing (I think it's not created yet).

How should I change the configuration?

Edit 1:

Here is the Dockerfile used to create the image:

# Database (http://www.cs3c.ma/)

FROM postgres:9.4
MAINTAINER Sabbane <[e-mail]>

ENV TERM=xterm

RUN apt-get update
RUN apt-get install -y nano

ADD scripts /scripts
# ADD scripts/setup-my-schema.sh /docker-entrypoint-initdb.d/

# Allow connections from anywhere.
RUN sed -i -e"s/^#listen_addresses =.*$/listen_addresses = '*'/" /var/lib/postgresql/data/postgresql.conf
RUN echo "host    all    all    0.0.0.0/0    md5" >> /var/lib/postgresql/data/pg_hba.conf

# Configure logs
RUN sed -i -e"s/^#logging_collector = off.*$/logging_collector = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_directory = 'pg_log'.*$/log_directory = '\/var\/log\/postgresql'/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_filename = 'postgresql-\%Y-\%m-\%d_\%H\%M\%S.log'.*$/log_filename = 'postgresql_\%a.log'/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_file_mode = 0600.*$/log_file_mode = 0644/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_truncate_on_rotation = off.*$/log_truncate_on_rotation = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_rotation_age = 1d.*$/log_rotation_age = 1d/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_min_duration_statement = -1.*$/log_min_duration_statement = 0/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_checkpoints = off.*$/log_checkpoints = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_connections = off.*$/log_connections = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_disconnections = off.*$/log_disconnections = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^log_line_prefix = '\%t \[\%p-\%l\] \%q\%u@\%d '.*$/log_line_prefix = '\%t \[\%p\]: \[\%l-1\] user=\%u,db=\%d'/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_lock_waits = off.*$/log_lock_waits = on/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#log_temp_files = -1.*$/log_temp_files = 0/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#statement_timeout = 0.*$/statement_timeout = 1800000        # in milliseconds, 0 is disabled (current 30min)/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^lc_messages = 'en_US.UTF-8'.*$/lc_messages = 'C'/" /var/lib/postgresql/data/postgresql.conf

# Performance Tuning
RUN sed -i -e"s/^max_connections = 100.*$/max_connections = 1000/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^shared_buffers =.*$/shared_buffers = 16GB/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#effective_cache_size = 128MB.*$/effective_cache_size = 48GB/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#work_mem = 1MB.*$/work_mem = 16MB/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#maintenance_work_mem = 16MB.*$/maintenance_work_mem = 2GB/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#checkpoint_segments = .*$/checkpoint_segments = 32/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#checkpoint_completion_target = 0.5.*$/checkpoint_completion_target = 0.7/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#wal_buffers =.*$/wal_buffers = 16MB/" /var/lib/postgresql/data/postgresql.conf
RUN sed -i -e"s/^#default_statistics_target = 100.*$/default_statistics_target = 100/" /var/lib/postgresql/data/postgresql.conf


VOLUME ["/var/lib/postgresql/data", "/var/log/postgresql"]

CMD ["postgres"]

With this Dockerfile the build process shows the error: sed: can't read /var/lib/postgresql/data/postgresql.conf: No such file or directory

Answer 1

When you run the official entrypoint (A.K.A. when you launch the container), it runs initdb in $PGDATA (/var/lib/postgresql/data by default), and then it stores in that directory these 2 files:

• postgresql.conf with default manual settings.
• postgresql.auto.conf with settings overriden automatically with ALTER SYSTEM commands.

The entrypoint also executes any /docker-entrypoint-initdb.d/*.{sh,sql} files.

All this means you can supply a shell/SQL script in that folder that configures the server for the next boot (which will be immediately after the DB initialization, or the next times you boot the container).

Example:

conf.sql file:

ALTER SYSTEM SET max_connections = 6;
ALTER SYSTEM RESET shared_buffers;

Dockerfile file:

FROM posgres:9.6-alpine
COPY *.sql /docker-entrypoint-initdb.d/
RUN chmod a+r /docker-entrypoint-initdb.d/*

And then you will have to execute conf.sql manually in already-existing databases. Since configuration is stored in the volume, it will survive rebuilds.

---

Another alternative is to pass -c flag as many times as you wish:

docker container run -d postgres -c max_connections=6 -c log_lock_waits=on

This way you don't need to build a new image, and you don't need to care about already-existing or not databases; all will be affected.