zot Clustering¶

High availability of the zot registry is supported by the following features:

Stateless zot instances to simplify scale out

Bare-metal and Kubernetes deployments

To ensure high-availability of the registry, zot supports a clustering scheme with stateless zot instances/replicas fronted by a loadbalancer and a shared remote backend storage. This scheme allows the registry service to remain available even if a few replicas fail or become unavailable. Loadbalancing across many zot replicas can also increase aggregate network throughput.

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Clustering is supported in both bare-metal and Kubernetes environments.

The remote backend storage must be S3 API-compatible.

Bare-metal deployment¶

Prerequisites¶

A highly-available loadbalancer such as HAProxy configured to direct traffic to zot replicas.
Multiple zot replicas as systemd services hosted on mutiple hosts or VMs.
AWS S3 API-compatible remote backend storage.

Kubernetes deployment¶

Prerequisites¶

A zot Kubernetes Deployment with required number of replicas.
AWS S3 API-compatible remote backend storage.
A zot Kubernetes Service.
A zot Kubernetes Ingress Gateway if the service needs to be exposed outside.

Implementing stateless zot¶

zot maintains two types of durable state:

the actual image data itself
the image metadata in the registry’s cache

In a stateless clustering scheme, the image data is stored in the remote storage backend and the registry cache is disabled by turning off both deduplication and garbage collection.

Ecosystem tools¶

The OCI Distribution Specification imposes certain rules about the HTTP URI paths to which various ecosystem tools must conform. Consider these rules when setting the HTTP prefixes during loadbalancing and ingress gateway configuration.

Examples¶

zot supports clustering by using multiple stateless zot replicas with shared S3 storage and an HAProxy (with sticky session) load-balancing traffic to the replicas.

YAML configuration¶

Click here to view a sample haproxy configuration.

global
        log /dev/log    local0
        log /dev/log    local1 notice
        chroot /var/lib/haproxy
        maxconn 2000
        stats socket /run/haproxy/admin.sock mode 660 level admin expose-fd listeners
        stats timeout 30s
        user haproxy
        group haproxy
        daemon

        # Default SSL material locations
        ca-base /etc/ssl/certs
        crt-base /etc/ssl/private

        # See: https://ssl-config.mozilla.org/#server=haproxy&server-version=2.0.3&config=intermediate
        ssl-default-bind-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
        ssl-default-bind-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
        ssl-default-bind-options ssl-min-ver TLSv1.2 no-tls-tickets

defaults
        log     global
        mode    http
        option  httplog
        option  dontlognull
        timeout connect 5000
        timeout client  50000
        timeout server  50000
        errorfile 400 /etc/haproxy/errors/400.http
        errorfile 403 /etc/haproxy/errors/403.http
        errorfile 408 /etc/haproxy/errors/408.http
        errorfile 500 /etc/haproxy/errors/500.http
        errorfile 502 /etc/haproxy/errors/502.http
        errorfile 503 /etc/haproxy/errors/503.http
        errorfile 504 /etc/haproxy/errors/504.http

frontend zot
    bind *:8080
    mode http
    default_backend zot-cluster

backend zot-cluster
    mode http
    balance roundrobin
    server zot1 127.0.0.1:8081 check
    server zot2 127.0.0.1:8082 check
    server zot3 127.0.0.1:8083 check

zot S3 configuration¶

Click here to view a sample zot configuration for S3.

{
    "distSpecVersion": "1.0.1-dev",
    "storage": {
        "rootDirectory": "/tmp/zot",
        "dedupe": true,
        "storageDriver": {
            "name": "s3",
            "rootdirectory": "/zot",
            "region": "us-east-2",
            "bucket": "zot-storage",
            "secure": true,
            "skipverify": false
        },
        "cacheDriver": {
            "name": "dynamodb",
            "endpoint": "http://localhost:4566",
            "region": "us-east-2",
            "tableName": "MainTable"
        }
    },
    "http": {
        "address": "127.0.0.1",
        "port": "8080"
    },
    "log": {
        "level": "debug"
    }
}

Last update: December 21, 2022