zookeeper

Zookeeper Backend

The Zookeeper backend enables confd to retrieve configuration data from Apache ZooKeeper, a distributed coordination service.

Configuration

Basic Connection

Connect to ZooKeeper:

confd zookeeper --node 127.0.0.1:2181 --onetime

Multiple nodes for high availability:

confd zookeeper \
  --node zk1.example.com:2181 \
  --node zk2.example.com:2181 \
  --node zk3.example.com:2181 --onetime

Options

Note: ZooKeeper authentication (SASL/Kerberos) is not currently supported by this backend.

Basic Example

Create znodes in ZooKeeper:

# Using zkCli.sh
zkCli.sh create /myapp ""
zkCli.sh create /myapp/database ""
zkCli.sh create /myapp/database/url "db.example.com"
zkCli.sh create /myapp/database/user "admin"
zkCli.sh create /myapp/database/password "secret123"

Or using the ZooKeeper shell:

[zk: localhost:2181(CONNECTED) 0] create /myapp ""
[zk: localhost:2181(CONNECTED) 1] create /myapp/database ""
[zk: localhost:2181(CONNECTED) 2] create /myapp/database/url "db.example.com"
[zk: localhost:2181(CONNECTED) 3] create /myapp/database/user "admin"
[zk: localhost:2181(CONNECTED) 4] create /myapp/database/password "secret123"

Create template resource (/etc/confd/conf.d/myapp.toml):

[template]
src = "myapp.conf.tmpl"
dest = "/etc/myapp/config.conf"
keys = [
  "/myapp/database",
]

Create template (/etc/confd/templates/myapp.conf.tmpl):

[database]
url = {{getv "/myapp/database/url"}}
user = {{getv "/myapp/database/user"}}
password = {{getv "/myapp/database/password"}}

Run confd:

confd zookeeper --node 127.0.0.1:2181 --onetime

Advanced Example

Service Discovery Pattern

Store service endpoints in ZooKeeper:

zkCli.sh create /services ""
zkCli.sh create /services/api ""
zkCli.sh create /services/api/node1 "10.0.1.100:8080"
zkCli.sh create /services/api/node2 "10.0.1.101:8080"
zkCli.sh create /services/api/node3 "10.0.1.102:8080"

Template for load balancer config:

upstream api {
{{range gets "/services/api/*"}}
    server {{.Value}};
{{end}}
}

Hierarchical Configuration

# Environment-specific config
zkCli.sh create /config ""
zkCli.sh create /config/production ""
zkCli.sh create /config/production/database ""
zkCli.sh create /config/production/database/host "prod-db.example.com"
zkCli.sh create /config/production/database/port "5432"

Template resource with prefix:

[template]
prefix = "/config/production"
src = "app.conf.tmpl"
dest = "/etc/app/config.conf"
keys = [
  "/database",
]

Kubernetes Deployment

apiVersion: v1
kind: Pod
metadata:
  name: myapp
spec:
  containers:
  - name: myapp
    command:
    - confd
    - zookeeper
    - --node=zk-0.zk-headless.default.svc:2181
    - --node=zk-1.zk-headless.default.svc:2181
    - --node=zk-2.zk-headless.default.svc:2181
    - --watch

Watch Mode Support

Watch mode is supported for the ZooKeeper backend. confd uses ZooKeeper's native watch mechanism for real-time updates.

confd zookeeper --node 127.0.0.1:2181 --watch

confd watches:

• Data changes: NodeDataChanged events on leaf nodes
• Child changes: NodeChildrenChanged events on parent nodes

When any watched znode changes, confd re-renders affected templates.

ZooKeeper Data Model

ZooKeeper uses a hierarchical namespace similar to a filesystem:

/
├── myapp
│   ├── database
│   │   ├── url = "db.example.com"
│   │   ├── user = "admin"
│   │   └── password = "secret"
│   └── cache
│       ├── host = "redis.example.com"
│       └── port = "6379"

• Znodes can have both data and children
• Leaf znodes (no children) store the actual configuration values
• Parent znodes are traversed recursively to find all values

Per-Resource Backend Configuration

Instead of using the global backend, individual template resources can specify their own ZooKeeper backend configuration. This allows mixing backends within a single confd instance.

Add a [backend] section to your template resource file:

[template]
src = "myapp.conf.tmpl"
dest = "/etc/myapp/config.conf"
keys = [
  "/myapp/database",
]

[backend]
backend = "zookeeper"
nodes = ["zk1.example.com:2181", "zk2.example.com:2181", "zk3.example.com:2181"]

Available backend options:

• backend - Must be "zookeeper"
• nodes - Array of ZooKeeper server addresses

Connection Behavior

• Session timeout: 1 second
• Automatic reconnection: ZooKeeper client handles reconnection automatically
• Ensemble support: Specify multiple nodes for automatic failover