Just wanna test things out? Here is an example command to run that doesn't require k8s.

docker run --rm -it --pid=host --privileged criticalstack/swoll:latest trace --no-containers -s execve,openat

Swoll is an experimental suite of applications and APIs for monitoring kernel-level activity on a live Kubernetes cluster, mostly written in the Golang programming language, strewn about with bits and bobs of C and Yaml.

Using simple counters and a minimal state, Swoll can report on a wide bevy of information on system calls being made by or from a container running inside a Kubernetes cluster. Each metric for both timing and counting contains the following information:

• Syscall
  • Return Status
  • Classification
  • Group
• Kubernetes information
  • Namespace
  • Pod
  • Container

Aggregating data in this manner allows a user to monitor every call and its resulting return status for every container in every Kubernetes Pod. For example, one can query the total count of calls to the function sys_openat sourced from a specific container in the pod coredns in the namespace kube-system that resulted in a "No such file or directory" error.

Metrics are exposed via the URI /metrics in Prometheus format, along with detailed charting examples (powered by e-charts) at the URI /metrics/charts.

Example charts output The above Sankey diagram displays the distribution of system calls in an attractive™ manner.

Example swoll top output

Prometheus query examples

$ promtool query instant https://prometheus.local '
  sort_desc(
   sum(
    swoll_node_metrics_syscall_count{
     namespace="kube-system"
    }) by (err))'

{err="ETIMEDOUT"}       => 745430
{err="EAGAIN"}          => 254506
{err="EINPROGRESS"}     => 2217
{err="EPERM"}           => 1779
{err="ENOENT"}          => 1288
{err="EPROTONOSUPPORT"} => 60
{err="EINTR"}           => 46

Total count of syscalls grouped by the return-status originating from the Kubernetes namespace kube-system

$ promtool query instant https://prometheus.local '
  sort_desc(
   sum(
    swoll_node_metrics_syscall_count{
     namespace="kube-system",
     syscall="sys_openat"
    }) by (namespace,pod))'

{namespace="kube-system", pod="kube-proxy-27xrc"}                 => 1260
{namespace="kube-system", pod="cilium-shskf"}                     => 670
{namespace="kube-system", pod="kube-apiserver-cinder"}            => 471
{namespace="kube-system", pod="coredns-7jhhg"}                    => 297
{namespace="kube-system", pod="kube-controller-manager-cinder"}   => 191
{namespace="kube-system", pod="cilium-operator-657978fb5b-cjx72"} => 78

Count all calls to the function sys_openat grouped by Kubernetes Pod, and namespace

$ promtool query instant https://prometheus.local '
  sort_desc(
   avg by (container, pod, namespace, syscall) (
    rate(
     swoll_node_metrics_syscall_count { err != "OK" }[5m]
     offset 5m
    )) /
   avg by (container, pod, namespace, syscall) (
    rate(
     swoll_node_metrics_syscall_count{ err != "OK" }[5m]
    )
   ))'
{container="operator", namespace="kube-system", pod="cilium-operator", syscall="sys_epoll_ctl"} => 2.0
{container="coredns",  namespace="kube-system", pod="coredns-7jhhg",   syscall="sys_futex"}     => 1.1
{container="operator", namespace="kube-system", pod="cilium-operator", syscall="sys_read"}      => 1.0
{container="agent",    namespace="kube-system", pod="cilium-shskf",    syscall="sys_futex"}     => 1.0

Query the relative change in the rate of calls that incurred an error compared to the previous 5 minutes grouped by container, Pod, namespace, and syscall

While metrics by themselves are great and all, swoll also provides a Kubernetes-native interface for creating, collecting, and presenting detailed real-time logs of system activity.

Take the following Trace configuration as an example:

apiVersion: tools.swoll.criticalstack.com/v1alpha1
kind: Trace
metadata:
  name: trace-nginx-hosts
  namespace: swoll
spec:
  syscalls:
    - connect
    - accept4
    - bind
    - listen
    - execve
    - openat
  labelSelector:
      matchLabels:
          app: "nginx"
  fieldSelector:
      matchLabels:
          status.phase: "Running"

When applied, swoll will start tracing the system-calls connect, accept4, bind, listen, execve, and openat for any containers that match the pod-label app=nginx, and the field-label status.phase=Running (match only running containers).

Once started, the raw JSON events are retrieved via kubectl logs:

$ kubectl logs -l sw-job=trace-nginx-hosts -n swoll | head -n 1 | jq .

{
  "payload": {
    "syscall": {
      "nr": 257,
      "name": "sys_openat",
      "class": "FileSystem",
      "group": "Files"
    },
    "pid": 3797092,
    "tid": 3797092,
    "uid": 0,
    "gid": 0,
    "comm": "sh",
    "session": 1,
    "container": {
      "id": "13765a70dfbb1b35ebff60c04ddfebf9177715bcf79e67279d4e8128799501bf",
      "pod": "nginx-provider",
      "name": "indexwriter",
      "image": "sha256:1510e850178318cd2b654439b56266e7b6cbff36f95f343f662c708cd51d0610",
      "namespace": "swoll",
      "labels": {
        "io.kubernetes.container.name": "indexwriter",
        "io.kubernetes.pod.name": "nginx-provider",
        "io.kubernetes.pod.namespace": "swoll",
        "io.kubernetes.pod.uid": "4c16fc49-2c47-427d-b5d6-a222e65b76c9"
      },
      "pid": 408510,
      "pid-namespace": 4026535150
    },
    "error": "OK",
    "return": 3,
    "pid_ns": 4026535150,
    "uts_ns": 4026535144,
    "mount_ns": 4026535149,
    "start": 529490506498247,
    "finish": 529490506535997,
    "args": {
      "dir_fd": -100,
      "pathname": "/html/index․html",
      "flags": [
        "O_CREAT",
        "O_APPEND",
        "O_WRONLY"
      ]
    }
  }
}

A sweet gif showing a trace running... So 2020

TBD, for now, see: `examples/'

See BUILD INSTRUCTIONS

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