Filter vbotka.freebsd.ast_to_haproxy

Synopsis 

The ast_to_haproxy filter translates an Abstract Syntax Tree (AST) structure into native HAProxy configuration syntax (haproxy.cfg). It is typically used in conjunction with dict_to_ast to generate configuration files from high-level YAML representations without relying on complex Jinja2 templates.

Parameters 

Parameter	Type	Default	Comments
_input	sequence / mapping		AST structure emitted by `dict_to_ast` or custom AST builders.
indent	integer	`4`	Number of spaces used for directive indentation inside sections.

Hint

View the documentation from the command line:

shell> ansible-doc -t filter vbotka.freebsd.ast_to_haproxy

Grammar & Transformations 

The filter applies several domain-specific normalizations to accommodate structured data trees:

Section Containers

Plural section dictionaries (frontends, backends, listens) are unwrapped into individual, singular top-level sections (frontend <name>, backend <name>, listen <name>).

Directives & Sub-groups

Options & Timeouts: Directives nested under options or timeouts maps are flattened to individual option <name> and timeout <name> <val> lines.

ACLs: Rules nested under acls are converted to acl <name> <criterion> <values...>.

Servers: Server records are inlined to standard server <name> <address> [check] [options] lines.

Routing: use_backends lists are rendered into single-line use_backend <backend> <condition> directives.

Boolean Normalization

Boolean parameters (True) are rendered as bare flags (e.g., daemon, httplog, check). Directives mapped to False or None are excluded from the output.

Examples 

Input Structured Data 

haproxy_config_data:
  global:
    log: /var/run/log local0
    maxconn: 4096
    user: nobody
    group: nobody
    daemon: true
  defaults:
    log: global
    mode: http
    retries: 3
    options:
      httplog: true
      dontlognull: true
    timeouts:
      connect: 5s
      client: 30s
      server: 30s
  frontends:
    http_front:
      bind: "*:80"
      acls:
        is_api: path_beg /api
      use_backends:
        - backend: api_servers
          condition: if is_api
      default_backend: web_servers
  backends:
    web_servers:
      balance: roundrobin
      servers:
        web1:
          address: 10.0.1.10:8080
          check: true
    api_servers:
      balance: roundrobin
      servers:
        api1:
          address: 10.0.2.10:8080
          check: true

Ansible Task Pipeline 

- name: Generate HAProxy configuration
  ansible.builtin.copy:
    dest: /usr/local/etc/haproxy.conf
    content: |
      {{ haproxy_config_data
         | vbotka.freebsd.dict_to_ast
         | vbotka.freebsd.ast_to_haproxy }}
    mode: '0644'
    validate: haproxy -c -f %s

Generated Configuration Output 

global
    log /var/run/log local0
    maxconn 4096
    user nobody
    group nobody
    daemon

defaults
    log global
    mode http
    retries 3
    option httplog
    option dontlognull
    timeout connect 5s
    timeout client 30s
    timeout server 30s

frontend http_front
    bind *:80
    acl is_api path_beg /api
    use_backend api_servers if is_api
    default_backend web_servers

backend web_servers
    balance roundrobin
    server web1 10.0.1.10:8080 check

backend api_servers
    balance roundrobin
    server api1 10.0.2.10:8080 check

Return Value 

Key	Type	Description
_value	string	The formatted HAProxy configuration string.