Troubleshooting the Installation of pg_cron in a Postgres Docker Container

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In this article, we will explore the challenges of installing the pg_cron extension in a Bitnami Postgres Docker container. We will delve into the configuration process and provide solutions to common issues that may arise during installation.

Understanding the Basics of pg_cron

The pg_cron extension is designed to manage scheduled jobs in PostgreSQL databases. It allows developers to schedule tasks to run at specific times or intervals, making it easier to automate repetitive tasks. However, like any other extension, its installation requires careful configuration and attention to detail.

The Error Message: “ERROR: extension ‘pg_cron’ must be installed in schema ‘pg_catalog’”

When trying to install the pg_cron extension in our Bitnami Postgres Docker container, we encounter an error message that reads:

“ERROR: extension ‘pg_cron’ must be installed in schema ‘pg_catalog’”

This error message indicates that the pg_cron extension cannot be installed directly in its default location. Instead, it requires installation in the pg_catalog schema.

The Role of Shared Preload Libraries

To resolve this issue, we need to configure PostgreSQL’s shared preload libraries. This setting allows us to load extensions dynamically without requiring a full restart of the server.

According to the error message, we must add pg_cron to the shared_preload_libraries configuration variable in PostgreSQL’s configuration file (postgresql.conf).

Modifying the postgresql.conf File

To modify the postgresql.conf file, we need to edit the Docker container’s configuration. Specifically, we need to update the environment variables set during container startup.

In our case, we have tried updating the configuration by adding the following command to the Dockerfile:

RUN echo "shared_preload_libraries='pg_cron'" >> /usr/share/postgresql/postgresql.conf.sample

However, this approach has proven to be insufficient. We need a more targeted solution that accounts for the container’s restart policy.

The Restart Policy: Resetting shared_preload_libraries

By default, Docker containers will reset environment variables and configuration files upon restart. This means that even if we update the postgresql.conf file, the changes will be lost during the next container start-up.

To address this issue, we need to find a way to persist our custom configuration across restarts. We can achieve this by using a combination of Docker’s built-in features and some creative workaround.

Solution: Using a Custom Configuration File

One approach is to create a custom configuration file that overrides the default postgresql.conf file during container startup.

Here’s an updated version of our Dockerfile:

FROM bitnami/postgresql:12

# Copy the updated postgresql.conf file
COPY postgresql_custom.conf /usr/share/postgresql/postgresql.conf.sample

# Create a custom configuration directory if it doesn't exist
RUN mkdir -p /etc/postgresql/12/main

# Update the environment variables and configuration files
ENV POSTGRES_DATA_DIR=/data
ENV POSTGRES_LOG_DIR=/logs
ENV POSTGRES_USER=myuser
ENV POSTGRES_PASSWORD=mypassword
RUN echo "shared_preload_libraries='pg_cron'" >> /usr/share/postgresql/postgresql.conf.sample

COPY postgresql_custom.conf /usr/share/postgresql/postgresql.conf.sample

In this example, we create a custom configuration file called postgresql_custom.conf that overrides the default postgresql.conf file. We also update the environment variables set during container startup.

The Final Step: Restarting and Verifying the Configuration

After applying these changes, restart our Docker container to verify that the updated configuration takes effect.

Once restarted, we can attempt to install the pg_cron extension using the following command:

CREATE EXTENSION pg_cron;

If everything is set up correctly, this should succeed without any errors.

Conclusion

Installing and configuring the pg_cron extension in a Bitnami Postgres Docker container requires attention to detail and some creative problem-solving. By understanding the basics of PostgreSQL extensions and configuration files, we can overcome common issues like shared preload libraries reset upon restart.

In conclusion, this article has demonstrated how to troubleshoot and resolve installation challenges for pg_cron in a Postgres Docker container. We hope that this information will be helpful to developers who encounter similar issues during their own projects.

Last modified on 2024-02-08