Middleware | Meta Intelligence Systems

Middleware

The layer between your application and the database. Pooling, load balancing, and failover are three separate jobs, and the common production mistake is expecting one component to do all three. These guides cover what each tool actually does, with configuration that runs.

How they connect

What each middleware tool depends on, replaces, or pairs with - including the databases and infrastructure it connects to outside this category.

Choose a starting point, then follow a recorded connection.

Use the map to decide what to read next: compare alternatives, look into a listed dependency or find a complementary tool. Lanes group entries by category and sort them alphabetically, so position does not signal importance or a reading order.

These are editorial recorded associations, not live topology or universal dependencies. Each arrow runs from the entry that records a relationship to the entry it names. It does not show traffic, execution order or a verified deployment.

Galera Cluster HAProxy keepalived Patroni PgBouncer Pgpool-II ProxySQL Asynchronous replication Cloud load balancer Envoy etcd Linux MariaDB nginx PgCat PostgreSQL repmgr

Dependency
Recorded use
Alternatives
Complements

This view shows 17 technologies joined by 53 directed records.

How to read this map

Every arrow points from the entry that owns a record to the entry it references. Reciprocal records stay separate, and the line pattern identifies the field, not strength or certainty. The linked guides give the context; a record on its own does not explain technical necessity.

Dependency (dependsOn): A lists B in dependsOn; check the guide for scope and configuration.
Recorded use (usedBy): A lists B in usedBy. This is not converted into a dependency claim about B.
Alternatives (alternatives): A lists B as an alternative to compare, not a guaranteed drop-in replacement.
Complements (complements): A lists B as a complement, not a requirement to deploy both.

A filled dot leads to a guide or concept explanation; a hollow dot leads to a relationship profile. The number on a card counts its direct records in this view. Selecting a card highlights only those direct records, not a transitive dependency tree.

Technologies appear when they have at least 1 outgoing record before filtering and belong to Middleware. Entries from other categories appear when a listed entry names them as a dependency, use, alternative or complement. Connections to entries outside this view are not drawn, so absence here does not mean that no relationship exists.

Text view: every displayed node and recorded connection

Each sentence names the record owner first, then the referenced entry. A connection appears under both endpoints for lookup, without reversing its meaning. This view and its links work without JavaScript.

Database

MariaDB Database

Open guide: MariaDB

9 direct recorded connections in this view. 4 further records touch entries outside this view.

Dependency / dependsOnGalera Cluster lists MariaDB as a dependency.
Complements / complementsGalera Cluster lists MariaDB as a complement.
Recorded use / usedByMariaDB records Galera Cluster in its usedBy list. This is a recorded use association, not an inferred dependency.
Recorded use / usedByMariaDB records ProxySQL in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsMariaDB lists Galera Cluster as a complement.
Complements / complementsMariaDB lists ProxySQL as a complement.
Complements / complementsMariaDB lists keepalived as a complement.
Dependency / dependsOnProxySQL lists MariaDB as a dependency.
Complements / complementsProxySQL lists MariaDB as a complement.

PostgreSQL Database

Open guide: PostgreSQL

11 direct recorded connections in this view. 23 further records touch entries outside this view.

Complements / complementsHAProxy lists PostgreSQL as a complement.
Dependency / dependsOnPatroni lists PostgreSQL as a dependency.
Dependency / dependsOnPgBouncer lists PostgreSQL as a dependency.
Dependency / dependsOnPgpool-II lists PostgreSQL as a dependency.
Complements / complementsPgpool-II lists PostgreSQL as a complement.
Recorded use / usedByPostgreSQL records PgBouncer in its usedBy list. This is a recorded use association, not an inferred dependency.
Recorded use / usedByPostgreSQL records Pgpool-II in its usedBy list. This is a recorded use association, not an inferred dependency.
Recorded use / usedByPostgreSQL records Patroni in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsPostgreSQL lists PgBouncer as a complement.
Complements / complementsPostgreSQL lists Patroni as a complement.
Complements / complementsPostgreSQL lists HAProxy as a complement.

Infrastructure

Cloud load balancer Infrastructure

Open relationship profile: Cloud load balancer

1 direct recorded connection in this view.

Alternatives / alternativeskeepalived lists Cloud load balancer as an alternative.

etcd Infrastructure

Open guide: etcd

3 direct recorded connections in this view. 9 further records touch entries outside this view.

Recorded use / usedByetcd records Patroni in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsetcd lists Patroni as a complement.
Dependency / dependsOnPatroni lists etcd as a dependency.

Middleware

Envoy Middleware

Open relationship profile: Envoy

1 direct recorded connection in this view. 1 further record touches an entry outside this view.

Alternatives / alternativesHAProxy lists Envoy as an alternative.

Galera Cluster Middleware

Open relationship profile: Galera Cluster

7 direct recorded connections in this view.

Dependency / dependsOnGalera Cluster lists MariaDB as a dependency.
Alternatives / alternativesGalera Cluster lists Asynchronous replication as an alternative.
Complements / complementsGalera Cluster lists MariaDB as a complement.
Complements / complementsGalera Cluster lists ProxySQL as a complement.
Recorded use / usedByMariaDB records Galera Cluster in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsMariaDB lists Galera Cluster as a complement.
Complements / complementsProxySQL lists Galera Cluster as a complement.

HAProxy Middleware

Open guide: HAProxy

15 direct recorded connections in this view.

Dependency / dependsOnHAProxy lists Linux as a dependency.
Alternatives / alternativesHAProxy lists nginx as an alternative.
Alternatives / alternativesHAProxy lists Envoy as an alternative.
Alternatives / alternativesHAProxy lists Pgpool-II as an alternative.
Complements / complementsHAProxy lists Patroni as a complement.
Complements / complementsHAProxy lists keepalived as a complement.
Complements / complementsHAProxy lists PgBouncer as a complement.
Complements / complementsHAProxy lists PostgreSQL as a complement.
Complements / complementskeepalived lists HAProxy as a complement.
Recorded use / usedByLinux records HAProxy in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsPatroni lists HAProxy as a complement.
Complements / complementsPgBouncer lists HAProxy as a complement.
Alternatives / alternativesPgpool-II lists HAProxy as an alternative.
Complements / complementsPostgreSQL lists HAProxy as a complement.
Alternatives / alternativesProxySQL lists HAProxy as an alternative.

Patroni Middleware

Open guide: Patroni

14 direct recorded connections in this view.

Recorded use / usedByetcd records Patroni in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsetcd lists Patroni as a complement.
Complements / complementsHAProxy lists Patroni as a complement.
Complements / complementskeepalived lists Patroni as a complement.
Dependency / dependsOnPatroni lists PostgreSQL as a dependency.
Dependency / dependsOnPatroni lists etcd as a dependency.
Alternatives / alternativesPatroni lists repmgr as an alternative.
Alternatives / alternativesPatroni lists Pgpool-II as an alternative.
Complements / complementsPatroni lists HAProxy as a complement.
Complements / complementsPatroni lists keepalived as a complement.
Complements / complementsPatroni lists PgBouncer as a complement.
Complements / complementsPgBouncer lists Patroni as a complement.
Recorded use / usedByPostgreSQL records Patroni in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsPostgreSQL lists Patroni as a complement.

PgBouncer Middleware

Open guide: PgBouncer

12 direct recorded connections in this view.

Complements / complementsHAProxy lists PgBouncer as a complement.
Complements / complementskeepalived lists PgBouncer as a complement.
Complements / complementsPatroni lists PgBouncer as a complement.
Dependency / dependsOnPgBouncer lists PostgreSQL as a dependency.
Alternatives / alternativesPgBouncer lists Pgpool-II as an alternative.
Alternatives / alternativesPgBouncer lists PgCat as an alternative.
Complements / complementsPgBouncer lists HAProxy as a complement.
Complements / complementsPgBouncer lists Patroni as a complement.
Complements / complementsPgBouncer lists keepalived as a complement.
Alternatives / alternativesPgpool-II lists PgBouncer as an alternative.
Recorded use / usedByPostgreSQL records PgBouncer in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsPostgreSQL lists PgBouncer as a complement.

PgCat Middleware

Open relationship profile: PgCat

1 direct recorded connection in this view.

Alternatives / alternativesPgBouncer lists PgCat as an alternative.

Pgpool-II Middleware

Open guide: Pgpool-II

8 direct recorded connections in this view.

Alternatives / alternativesHAProxy lists Pgpool-II as an alternative.
Alternatives / alternativesPatroni lists Pgpool-II as an alternative.
Alternatives / alternativesPgBouncer lists Pgpool-II as an alternative.
Dependency / dependsOnPgpool-II lists PostgreSQL as a dependency.
Alternatives / alternativesPgpool-II lists PgBouncer as an alternative.
Alternatives / alternativesPgpool-II lists HAProxy as an alternative.
Complements / complementsPgpool-II lists PostgreSQL as a complement.
Recorded use / usedByPostgreSQL records Pgpool-II in its usedBy list. This is a recorded use association, not an inferred dependency.

Middleware (continued)

ProxySQL Middleware

Open relationship profile: ProxySQL

7 direct recorded connections in this view. 1 further record touches an entry outside this view.

Complements / complementsGalera Cluster lists ProxySQL as a complement.
Recorded use / usedByMariaDB records ProxySQL in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsMariaDB lists ProxySQL as a complement.
Dependency / dependsOnProxySQL lists MariaDB as a dependency.
Alternatives / alternativesProxySQL lists HAProxy as an alternative.
Complements / complementsProxySQL lists MariaDB as a complement.
Complements / complementsProxySQL lists Galera Cluster as a complement.

keepalived Middleware

Open guide: keepalived

10 direct recorded connections in this view.

Complements / complementsHAProxy lists keepalived as a complement.
Dependency / dependsOnkeepalived lists Linux as a dependency.
Alternatives / alternativeskeepalived lists Cloud load balancer as an alternative.
Complements / complementskeepalived lists HAProxy as a complement.
Complements / complementskeepalived lists Patroni as a complement.
Complements / complementskeepalived lists PgBouncer as a complement.
Recorded use / usedByLinux records keepalived in its usedBy list. This is a recorded use association, not an inferred dependency.
Complements / complementsMariaDB lists keepalived as a complement.
Complements / complementsPatroni lists keepalived as a complement.
Complements / complementsPgBouncer lists keepalived as a complement.

nginx Middleware

Open relationship profile: nginx

1 direct recorded connection in this view.

Alternatives / alternativesHAProxy lists nginx as an alternative.

repmgr Middleware

Open relationship profile: repmgr

1 direct recorded connection in this view.

Alternatives / alternativesPatroni lists repmgr as an alternative.

Pattern

Asynchronous replication Pattern

Open relationship profile: Asynchronous replication

1 direct recorded connection in this view.

Alternatives / alternativesGalera Cluster lists Asynchronous replication as an alternative.

Systems

Linux Systems

Open guide: Linux

4 direct recorded connections in this view. 31 further records touch entries outside this view.

Dependency / dependsOnHAProxy lists Linux as a dependency.
Dependency / dependsOnkeepalived lists Linux as a dependency.
Recorded use / usedByLinux records HAProxy in its usedBy list. This is a recorded use association, not an inferred dependency.
Recorded use / usedByLinux records keepalived in its usedBy list. This is a recorded use association, not an inferred dependency.

Guides

Pooling & proxying

PgBouncer

PostgreSQL connection pooling with PgBouncer - pool modes and what each one breaks, sizing the pool, secure auth_query, and running it multi-core.

Read

Pgpool-II

Pgpool-II in practice - clustering modes, how load balancing decides where a SELECT goes, watchdog quorum, failover, and the diagnostics.

Read

HA & load balancing

Patroni

How Patroni fails PostgreSQL over - the DCS leader lock, the ttl/loop_wait/retry_timeout rule, watchdog fencing, and a runnable three-node config.

Read

keepalived

VRRP master election in keepalived - a runnable two-node config, the weight arithmetic people get wrong, and why it fails on cloud networks.

Read

HAProxy for PostgreSQL

A runnable HAProxy configuration for a three-node Patroni cluster - mode tcp, Patroni HTTP health checks, timeouts for long-lived sessions, and draining.

Read

Coordination & observability

etcd

Raft, quorum and leases in etcd, the fsync latency budget that decides cluster stability, and the space-quota outage - compaction, defragmentation, recovery.

Read

Prometheus

The pull model, why a label set defines a time series and cardinality kills servers, histogram versus summary, rate() correctly, and Alertmanager routing.

Read