Fluent Bit with containerd, CRI-O and JSON

With dockerd deprecated as a Kubernetes container runtime, we moved to containerd. After the change, our fluentbit logging didn't parse our JSON logs correctly. containerd and CRI-O use the CRI Log format which is slightly different and requires additional parsing to parse JSON application logs.

We couldn't find a good end-to-end example, so we created this from various GitHub issues. There are some features missing (like multi-line logs) and we love PRs.

Enhancement

The original version of this repo used a separate filter to parse the JSON. By changing the cri parser to use the log field instead of the message field, the kubernetes filter converts the JSON if Merge_Log is set to On

We also had to add two nest filters to the config to lift the Kubernetes values to the root level.

Sample Config

config.yaml contains a complete and minimal example configuration using stdout. We have tested with stdout and Azure Log Analytics. While not tested, it should work with Elastic Search and outher output providers as well.

You will need to change the output match from myapp*.*

Config Changes

Note - there are several GitHub discussions on the challenges with multi-line CRI Logs - additional processing is necessary and not included here

In config there are three changes:

Add the CRI parser which is a regex parser that maps the CRI Log fields into time stream logtag and log
- time and stream map to existing dockerd log fields
- log contains the text of the message, which, in our case is JSON
  - The JSON is parsed and merged in the kubernetes filter
    - Merge_Log must be set to On

Note the regex expression uses log for the 4th field, not message

[PARSER]
    Name        cri
    Format      regex
    Regex       ^(?<time>[^ ]+) (?<stream>stdout|stderr) (?<logtag>[^ ]*) (?<log>.*)$
    Time_Key    time
    Time_Format %Y-%m-%dT%H:%M:%S.%L%z

Add the nest filters to lift the Kubernetes values to the root document

    [FILTER]
        Name          nest
        Match         kube.*
        Operation     lift
        Nested_under  kubernetes
        Add_prefix    kubernetes_

    [FILTER]
        Name          nest
        Match         kube.*
        Operation     lift
        Nested_under  kubernetes_labels
        Add_prefix    kubernetes_labels_

Change the Parser on the input from json or docker to cri

[INPUT]
    Name              tail
    Tag               kube.*
    Path              /var/log/containers/*.log
    Parser            cri

Attribution

Thank you!

We copied a lot of the yaml from several different GitHub issues / docs including fluentbit docs

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