---
title: "Using channels in configuration objects"
url: "https://axoflow.com/docs/axosyslog-core/4.28/chapter-configuration-file/embedded-objects/"
last_modified: "2023-07-02T20:37:04+02:00"
---

> For the complete documentation index, see [llms.txt](https://axoflow.com/docs/axosyslog-core/4.28/llms.txt).

# Using channels in configuration objects

Starting with AxoSyslog 3.4, every configuration object is a log expression. Every configuration object is essentially a configuration block, and can include multiple objects. To reference the block, only the top-level object must be referenced. That way you can use embedded log statements, junctions and in-line object definitions within source, destination, filter, rewrite and parser definitions. For example, a source can include a rewrite rule to modify the messages received by the source, and that combination can be used as a simple source in a log statement. This feature allows you to preprocess the log messages very close to the source itself.

To embed multiple objects into a configuration object, use the following syntax. Note that you must enclose the configuration block between braces instead of parenthesis.

```shell
   <type-of-top-level-object> <name-of-top-level-object> {
        channel {
            <configuration-objects>
        };
    };
```

## Example: Using channels

For example, to process a log file in a specific way, you can define the required processing rules (parsers and rewrite expressions) and combine them in a single object:

```shell
   source s_apache {
        channel {
            source {
                file("/var/log/apache/error.log");
            };
            parser(p_apache_parser);
        };
    };
    log {
        source(s_apache); ...
    };
```

The `s_apache` source uses a file source (the error log of an Apache webserver) and references a specific parser to process the messages of the error log. The log statement references only the `s_apache` source, and any other object in the log statement can already use the results of the `p_apache_parser`parser.

> **Note:**
>
> You must start the object definition with a `channel` even if you will use a `junction`, for example:
>
> ```shell
>    parser demo-parser() {
>         channel {
>             junction {
>                 channel { ... };
>                 channel { ... };
>             };
>         };
>     };
> ```
>
> If you want to embed configuration objects into sources or destinations, always use channels, otherwise the source or destination will not behave as expected. For example, the following configuration is good:
>
> ```shell
>    source s_filtered_hosts {
>         channel{
>             source {
>                 pipe("/dev/pipe");
>                 syslog(ip(192.168.0.1) transport("tcp"));
>                 syslog(ip(127.0.0.1) transport("tcp"));
>             };
>             filter {
>                 netmask(10.0.0.0/16);
>             };
>         };
>     };
> ```

Last modified July 2, 2023: [Change highlight mode of code examples (2f8a9593)](https://github.com/axoflow/axosyslog-core-docs/commit/2f8a95937c6498193e7168ce8b0dc831e9f0f8ad)