How to Fix PostgreSQL 16 Dockerfile Error: "pg_dump: error: aborting because of server version mismatch"

While Docker offers a structured approach to package dependencies, ensuring compatibility across versions can be a frustrating journey, especially when dealing with specific tools like PostgreSQL clients. This blog post dives into a real-world challenge faced when trying to install a PostgreSQL client within a Dockerfile, highlighting the pitfalls and ultimately showcasing a solution for achieving the desired version compatibility.

The Problem: A Clash of Versions

The starting point of our adventure is a Dockerfile that utilizes the mcr.microsoft.com/dotnet/aspnet:8.0 image as its base. The goal is straightforward: install the PostgreSQL client to enable interaction with a PostgreSQL server. This is achieved through the following line:

      RUN apt-get update && apt-get install -y --no-install-recommends postgresql-client
    

This command, while seemingly innocuous, leads to a frustrating outcome. Upon execution, a clear error message emerges:

pg_dump: pg_dump: error: aborting because of server version mismatch
pg_dump: pg_dump: detail: server version: 16.1 (Debian 16.1-1.pgdg120+1); pg_dump version: 15.6 (Debian 15.6-0+deb12u1)
    

The error points to a discrepancy between the server's PostgreSQL version (16.1) and the installed client version (15.6). While the client installation succeeded, it yielded an incompatible version, rendering the tools useless.

The Quest for a Specific Version

The natural instinct is to attempt a direct installation of the desired version, postgresql-client-16:

      RUN apt-get update && apt-get install -y --no-install-recommends postgresql-client-16
    

However, this effort is met with a disheartening message:

      Unable to locate package postgresql-client-16
    

The package is simply unavailable in the standard package repositories.

Adding the official PostgreSQL repository to the mix proves to be equally ineffective. This involves steps like:

RUN apt-get update && apt-get install -y wget gnupg2
RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | gpg --dearmor -o /usr/share/keyrings/postgresql.gpg
RUN echo "deb [signed-by=/usr/share/keyrings/postgresql.gpg] http://apt.postgresql.org/pub/repos/apt/ bullseye-pgdg main" > /etc/apt/sources.list.d/pgdg.list
RUN apt-get update && apt-get install -y --no-install-recommends postgresql-client-16
    

While this successfully adds the PostgreSQL repository, attempting to install the client again results in a different set of dependency issues:

      postgresql-client-16 : Depends: libpq5 (>= 16.2) but it is not going to be installed
                       Depends: libssl1.1 (>= 1.1.0) but it is not installable
    

The installation is hampered by missing dependencies, namely libpq5 and libssl1.1. Trying to install these libraries independently yields further errors, suggesting a deeper incompatibility within the Docker image.

Finding the Solution: A Change of Base

The root of the issue lies in the chosen base image, mcr.microsoft.com/dotnet/aspnet:8.0. The specific version of the PostgreSQL client included in this image is incompatible with the target server version. To address this fundamental incompatibility, a shift in strategy is necessary:

• Utilize an Alternative Base Image: Instead of relying on the standard mcr.microsoft.com/dotnet/aspnet:8.0 base, we'll switch to the mcr.microsoft.com/dotnet/aspnet:8.0-alpine image. This Alpine-based image provides a version of the PostgreSQL client that harmonizes with PostgreSQL server version 16.

The updated Dockerfile now looks like this:

FROM mcr.microsoft.com/dotnet/aspnet:8.0-alpine as base

RUN apk add --no-cache postgresql-client

CMD pg_dump --version
    

This concise approach avoids the complex dependency headaches encountered earlier. The apk add command seamlessly installs the required PostgreSQL client package within the Alpine environment.

Verification and Validation

To confirm the success of this solution, the CMD instruction is added to the Dockerfile. It explicitly invokes the pg_dump command with the --version flag, providing a clear indication of the installed client version:

      pg_dump (PostgreSQL) 16.2
    

The output confirms that the installed PostgreSQL client version is 16.2, perfectly aligned with the target PostgreSQL server version.

Conclusion

The journey to install the PostgreSQL client within a Docker image revealed a crucial lesson: dependency management is paramount. The seemingly straightforward installation process unveiled a complex web of version compatibility issues, necessitating a careful selection of the base image to achieve harmonious coexistence.

By adopting the mcr.microsoft.com/dotnet/aspnet:8.0-alpine base image and leveraging the apk add command, we successfully circumvented the dependency conflicts and achieved a compatible PostgreSQL client installation. This streamlined solution provides a practical demonstration of how understanding base image variations and utilizing appropriate package management tools can be crucial for achieving stability and compatibility in a containerized environment.