postgres: PostgreSQL module for NGINX

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

• RedHat Enterprise Linux 7, 8, 9
• CentOS 7, 8, 9
• AlmaLinux 8, 9
• Rocky Linux 8, 9
• Amazon Linux 2 and Amazon Linux 2023

CentOS/RHEL 7 and Amazon Linux 2CentOS/RHEL 8, 9 and Fedora Linux, Amazon Linux 2023, etc.

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install nginx-module-postgres

dnf -y install https://extras.getpagespeed.com/release-latest.rpm 
dnf -y install nginx-module-postgres

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_postgres_module.so;

This document describes nginx-module-postgres v1.0 released on Aug 22 2020.

---

ngx_postgres is an upstream module that allows nginx to communicate directly with PostgreSQL database.

Response is generated in rds format, so it's compatible with ngx_rds_json and ngx_drizzle modules.

Status

This module is production-ready and it's compatible with following nginx releases:

• 0.7.x (tested with 0.7.60 to 0.7.69),
• 0.8.x (tested with 0.8.0 to 0.8.55),
• 0.9.x (tested with 0.9.0 to 0.9.7),
• 1.0.x (tested with 1.0.0 to 1.0.11),
• 1.1.x (tested with 1.1.0 to 1.1.12).
• 1.2.x (tested with 1.2.3 to 1.2.3).
• 1.3.x (tested with 1.3.4 to 1.3.4).

Configuration directives

postgres_server

• syntax: postgres_server ip[:port] dbname=dbname user=user password=pass
• default: none
• context: upstream

Set details about the database server.

postgres_keepalive

• syntax: postgres_keepalive off | max=count [mode=single|multi] [overflow=ignore|reject]
• default: max=10 mode=single overflow=ignore
• context: upstream

Configure keepalive parameters:

• max - maximum number of keepalive connections (per worker process),
• mode - backend matching mode,
• overflow - either ignore the fact that keepalive connection pool is full and allow request, but close connection afterwards or reject request with 503 Service Unavailable response.

postgres_pass

• syntax: postgres_pass upstream
• default: none
• context: location, if location

Set name of an upstream block that will be used for the database connections (it can include variables).

postgres_query

• syntax: postgres_query [methods] query
• default: none
• context: http, server, location, if location

Set query string (it can include variables). When methods are specified then query is used only for them, otherwise it's used for all methods.

This directive can be used more than once within same context.

postgres_rewrite

• syntax: postgres_rewrite [methods] condition [=]status_code
• default: none
• context: http, server, location, if location

Rewrite response status_code when given condition is met (first one wins!):

• no_changes - no rows were affected by the query,
• changes - at least one row was affected by the query,
• no_rows - no rows were returned in the result-set,
• rows - at least one row was returned in the result-set.

When status_code is prefixed with = sign then original response body is send to the client instead of the default error page for given status_code.

By design both no_changes and changes apply only to INSERT, UPDATE, DELETE, MOVE, FETCH and COPY SQL queries.

This directive can be used more than once within same context.

postgres_output

• syntax: postgres_output rds|text|value|binary_value|none
• default: rds
• context: http, server, location, if location

Set output format:

• rds - return all values from the result-set in rds format (with appropriate Content-Type),
• text - return all values from the result-set in text format (with default Content-Type), values are separated by new line,
• value - return single value from the result-set in text format (with default Content-Type),
• binary_value - return single value from the result-set in binary format (with default Content-Type),
• none - don't return anything, this should be used only when extracting values with postgres_set for use with other modules (without Content-Type).

postgres_set

• syntax: postgres_set $variable row column [optional|required]
• default: none
• context: http, server, location

Get single value from the result-set and keep it in $variable.

When requirement level is set to required and value is either out-of-range, NULL or zero-length, then nginx returns 500 Internal Server Error response. Such condition is silently ignored when requirement level is set to optional (default).

Row and column numbers start at 0. Column name can be used instead of column number.

This directive can be used more than once within same context.

postgres_escape

• syntax: postgres_escape $escaped [[=]$unescaped]
• default: none
• context: http, server, location

Escape and quote $unescaped string. Result is stored in $escaped variable which can be safely used in SQL queries.

Because nginx cannot tell the difference between empty and non-existing strings, all empty strings are by default escaped to NULL value. This behavior can be disabled by prefixing $unescaped string with = sign.

postgres_connect_timeout

• syntax: postgres_connect_timeout timeout
• default: 10s
• context: http, server, location

Set timeout for connecting to the database.

postgres_result_timeout

• syntax: postgres_result_timeout timeout
• default: 30s
• context: http, server, location

Set timeout for receiving result from the database.

Configuration variables

$postgres_columns

Number of columns in received result-set.

$postgres_rows

Number of rows in received result-set.

$postgres_affected

Number of rows affected by INSERT, UPDATE, DELETE, MOVE, FETCH or COPY SQL query.

$postgres_query

SQL query, as seen by PostgreSQL database.

Sample configurations

Sample configuration #1

Return content of table cats (in rds format).

http {
    upstream database {
        postgres_server  127.0.0.1 dbname=test
                         user=test password=test;
    }

    server {
        location / {
            postgres_pass   database;
            postgres_query  "SELECT * FROM cats";
        }
    }
}

Sample configuration #2

Return only those rows from table sites that match host filter which is evaluated for each request based on its $http_host variable.

http {
    upstream database {
        postgres_server  127.0.0.1 dbname=test
                         user=test password=test;
    }

    server {
        location / {
            postgres_pass   database;
            postgres_query  SELECT * FROM sites WHERE host='$http_host'";
        }
    }
}

Sample configuration #3

Pass request to the backend selected from the database (traffic router).

http {
    upstream database {
        postgres_server  127.0.0.1 dbname=test
                         user=test password=test;
    }

    server {
        location / {
            eval_subrequest_in_memory  off;

            eval $backend {
                postgres_pass    database;
                postgres_query   "SELECT * FROM backends LIMIT 1";
                postgres_output  value 0 0;
            }

            proxy_pass  $backend;
        }
    }
}

Required modules (other than ngx_postgres):

• nginx-eval-module (agentzh's fork),

Sample configuration #4

Restrict access to local files by authenticating against PostgreSQL database.

http {
    upstream database {
        postgres_server  127.0.0.1 dbname=test
                         user=test password=test;
    }

    server {
        location = /auth {
            internal;

            postgres_escape   $user $remote_user;
            postgres_escape   $pass $remote_passwd;

            postgres_pass     database;
            postgres_query    "SELECT login FROM users WHERE login=$user AND pass=$pass";
            postgres_rewrite  no_rows 403;
            postgres_output   none;
        }

        location / {
            auth_request      /auth;
            root              /files;
        }
    }
}

Required modules (other than ngx_postgres):

• ngx_http_auth_request_module,
• ngx_coolkit.

Sample configuration #5

Simple RESTful webservice returning JSON responses with appropriate HTTP status codes.

http {
    upstream database {
        postgres_server  127.0.0.1 dbname=test
                         user=test password=test;
    }

    server {
        set $random  123;

        location = /numbers/ {
            postgres_pass     database;
            rds_json          on;

            postgres_query    HEAD GET  "SELECT * FROM numbers";

            postgres_query    POST      "INSERT INTO numbers VALUES('$random') RETURNING *";
            postgres_rewrite  POST      changes 201;

            postgres_query    DELETE    "DELETE FROM numbers";
            postgres_rewrite  DELETE    no_changes 204;
            postgres_rewrite  DELETE    changes 204;
        }

        location ~ /numbers/(?<num>\d+) {
            postgres_pass     database;
            rds_json          on;

            postgres_query    HEAD GET  "SELECT * FROM numbers WHERE number='$num'";
            postgres_rewrite  HEAD GET  no_rows 410;

            postgres_query    PUT       "UPDATE numbers SET number='$num' WHERE number='$num' RETURNING *";
            postgres_rewrite  PUT       no_changes 410;

            postgres_query    DELETE    "DELETE FROM numbers WHERE number='$num'";
            postgres_rewrite  DELETE    no_changes 410;
            postgres_rewrite  DELETE    changes 204;
        }
    }
}

Required modules (other than ngx_postgres):

• ngx_rds_json.

Sample configuration #6

Use GET parameter in SQL query.

location /quotes {
    set_unescape_uri  $txt $arg_txt;
    postgres_escape   $txt;
    postgres_pass     database;
    postgres_query    "SELECT * FROM quotes WHERE quote=$txt";
}

Required modules (other than ngx_postgres):

• ngx_set_misc.

Testing

ngx_postgres comes with complete test suite based on Test::Nginx.

You can test core functionality by running:

$ TEST_NGINX_IGNORE_MISSING_DIRECTIVES=1 prove

You can also test interoperability with following modules:

• ngx_coolkit,
• ngx_echo,
• ngx_form_input,
• ngx_set_misc,
• ngx_http_auth_request_module,
• nginx-eval-module (agentzh's fork),
• ngx_rds_json.

by running:

$ prove

See also

• ngx_rds_json,
• ngx_drizzle,
• ngx_lua,
• nginx-eval-module (agentzh's fork).

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-postgres.