Background: I use glog to register signal handler, but it cannot kill the init process (PID=1) with kill sigcall. That way, even though deadly signals like SIGABRT is raised, kubernetes controller manager won't be able to understand the pod is actually not functioning, thus kill the pod and restart a new one.
My idea is to add logic into my readiness/liveness probe: check the content for current container, whether it's in healthy state.
I'm trying to look into the logs on container's local filesystem /var/log, but haven't found anything useful.
I'm wondering if it's possible to issue a HTTP request to somewhere, to get the complete log? I assume it's stored somewhere.
You can find the kubernetes logs on Master machine at:
/var/log/pods
if using docker containers:
/var/lib/docker/containers
Containers are Ephemeral
Docker containers emit logs to the stdout and stderr output streams. Because containers are stateless, the logs are stored on the Docker host in JSON files by default.
The default logging driver is json-file. The logs are then annotated with the log origin, either stdout or stderr, and a timestamp. Each log file contains information about only one container.
As #Uri Loya said, You can find these JSON log files in /var/lib/docker/containers/ directory on a Linux Docker host. Here's how you can access them:
/var/lib/docker/containers/<container id>/<container id>-json.log
You can collect the logs with a log aggregator and store them in a place where they'll be available forever. It's dangerous to keep logs on the Docker host because they can build up over time and eat into your disk space. That's why you should use a central location for your logs and enable log rotation for your Docker containers.
Related
When I type kubectl log pod/yourpod to get my pod's logs, behind the scene, k8s must read the log from somewhere in my pod.
What's the default path to the log generated by my container?
How to change the path?
Inside my container, my process uses sigs.k8s.io/controller-runtime/pkg/log to generate logs.
It is the console output (stdout / stderr) that is captured by the container runtime and made available by the kubelet running on the node to the API server.
So there is not real log file, though the container runtime usually has a means of buffering the logs to the file system.
Is there an dynamic way to pull log data from inside my containers?
All of my searches are returning that Azure Logs/Azure Sentinel can read data about AKS relative to the containers as they exist in K8s (online, running, failed, etc.) but not the actual in-container logs. Examples of results asking for this:
https://learn.microsoft.com/en-us/azure/azure-monitor/containers/container-insights-log-query
https://learn.microsoft.com/en-us/azure/azure-monitor/containers/container-insights-livedata-overview
https://github.com/MicrosoftDocs/azure-docs/blob/main/articles/azure-monitor/containers/container-insights-enable-new-cluster.md#enable-monitoring-of-a-new-azure-kubernetes-service-aks-cluster
...all of these provide documentation on monitoring containers (as they live in K8s) but not the app-level logs in the containers...
Is anyone aware of a technology or capability for Azure Logs/Azure Sentinel to consume in-container, on-disk container logs (e.g. inside the container: /var/log, /var/application/logs, etc.)?
Thanks!
Assuming you're referring to linux containers. You only need to have have the OMS agent enabled and pointing to the right workspace and this gets the logs streamed over easily.
The ContainerLog table which would show you the same thing as kubectl logs <pod>. Anything that's sent to stdout and stderr from your container should be available in the Log Analytics Workspace. So if these are not being sent to either, you could just write a small script as part of your container, that would send those logs to stdout.
Here's how I'm able to get SMTP logs from my container:
How to force all kubernetes services (proxy, kublet, apiserver..., containers) to write logs to /var/logs?
For example:
/var/logs/apiServer.log
or:
/var/logs/proxy.log
Can I use syslog config to do that? What would be an example of that config?
I have already tried journald configuration forward to syslogs=yes.
Just first what comes to my mind - create sidecar container that will gather all the logs in 1 place.
The Complete Guide to Kubernetes Logging.
That's a pretty wide question that should be divided on few parts. Kubernets stores different types of logs in different places.
Kubernetes Container Logs (out of this question, but simply kubectl logs <podname> + -n for namespace, if its not default + -c for specifying container inside the pod)
Kubernetes Node Logs
Kubernetes Cluster Logs
Kubernetes Node Logs
Depending on your operating system and services, there are various
node-level logs you can collect, such as kernel logs or systemd logs.
On nodes with systemd both the kubelet and container runtime write to
journald. If systemd is not present, they write to .log files in the
/var/log directory.
You can access systemd logs with the journalctl command.
Tutorial: Logging with journald have a huge explanation how can you configure journalctl to gather logs. With agrregation logs tools like ELK and without them. journald log filtering can simplify your life.
There are two ways of centralizing journal entries via syslog:
syslog daemon acts as a journald client (like journalctl or Logstash or Journalbeat)
journald forwards messages to syslog (via socket)
Option 1) is slower – reading from the journal is slower than reading from the socket – but captures all the fields from the journal.
Option 2) is safer (e.g. no issues with journal corruption), but the journal will only forward traditional syslog fields (like severity, hostname, message..)
Talking about ForwardToSyslog=yes in /etc/systemd/journald.conf --> it will write messages, in syslog format, to /run/systemd/journal/syslog. You can pass processing then this file to rsyslog for example. Either you can manually process logs or move them to desired place..
Kubernetes Cluster Logs
By default, system components outside a container write files to journald, while components running in containers write to /var/log directory. However, there is the option to configure the container engine to stream logs to a preferred location.
Kubernetes doesn’t provide a native solution for logging at cluster level. However, there are other approaches available to you:
Use a node-level logging agent that runs on every node
Add a sidecar container for logging within the application pod
Expose logs directly from the application.
P.S. I have NOT tried below approach, but it looks promising - check it and maybe it will help you in your not easiest task.
The easiest way of setting up a node-level logging agent is to
configure a DaemonSet to run the agent on each node
helm install --name st-agent \
--set infraToken=xxxx-xxxx \
--set containerToken=xxxx-xxxx \
--set logsToken=xxxx-xxxx \
--set region=US \
stable/sematext-agent
This setup will, by default, send all cluster and container logs to a
central location for easy management and troubleshooting. With a tiny
bit of added configuration, you can configure it to collect node-level
logs and audit logs as well.
kubectl logs -f <pod-name>
This command shows the logs from the container log file.
Basically, I want to check the difference between "what is generated by the container" and "what is written to the log file".
I see some unusual binary logs, so I just want to find out if the container is creating those binary logs or the logs are not properly getting written to the log file.
"Unusual logs":
\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\
Usually, containerized applications, do not write to the log files but send messages to stdout/stderr, there is no point in storing log files inside containers, as they will be deleted when the pod is deleted.
What you see when running
kubectl logs -f <pod-name>
are messages sent to stdout/stderr. There are no container specific logs here, only application logs.
If, for some reason, your application does write to the log file, you can check it by execing into pod with e.g.
kubectl exec -it <pod-name> -- /bin/bash
and read logs as you would in shell.
Edit
Application logs
A container engine handles and redirects any output generated to a containerized application's stdout and stderr streams. For example, the Docker container engine redirects those two streams to a logging driver, which is configured in Kubernetes to write to a file in JSON format.
Those logs are also saved to
/var/log/containers/
/var/log/pods/
By default, if a container restarts, the kubelet keeps one terminated container with its logs. If a pod is evicted from the node, all corresponding containers are also evicted, along with their logs.
Everything you see by issuing the command
kubectl logs <pod-name>
is what application sent to stdout/stderr, or what was redirected to stdout/stderr. For example nginx:
The official nginx image creates a symbolic link from /var/log/nginx/access.log to /dev/stdout, and creates another symbolic link from /var/log/nginx/error.log to /dev/stderr, overwriting the log files and causing logs to be sent to the relevant special device instead.
Node logs
Components that do not run inside containers (e.g kubelet, container runtime) write to journald. Otherwise, they write to .log fies inside /var/log/ directory.
Excerpt from official documentation:
For now, digging deeper into the cluster requires logging into the relevant machines. Here are the locations of the relevant log files. (note that on systemd-based systems, you may need to use journalctl instead)
Master
/var/log/kube-apiserver.log - API Server, responsible for serving the API
/var/log/kube-scheduler.log - Scheduler, responsible for making scheduling decisions
/var/log/kube-controller-manager.log - Controller that manages replication controllers
Worker Nodes
/var/log/kubelet.log - Kubelet, responsible for running containers on the node
/var/log/kube-proxy.log - Kube Proxy, responsible for service load balancing
The only way I could imagine this to work is to make use of some external logging facility like Syslog or Elastisearch or anything else. Configure your application to send logs directly to logging facility (avoiding agents like fluentd or logstash which parse logs from files).
All modern languages have support for external logging. You can also configure Docker to send logs to syslog server.
Simple way to check log is kubernets:
=> If pod have single container
kubectl logs POD_NAME
=> If pod have multiple containers
kubectl logs POD_NAME -c CONTAINER_NAME -n NAMESPACE
I am pretty sure it writes it on disk somewhere. Otherwise if the container runs for several hours and logs a lot, then it would exceed what the stderr can hold I think. No?
Is it possible to compress and download the logs of kubectl logs?i.e. comparess on the container without downloading them?
Firstly take a look on logging-kubernetes official documentation.
In most cases, Docker container logs are put in the /var/log/containers directory on your host (host they are deployed on). Docker supports multiple logging drivers but Kubernetes API does not support driver configuration.
Once a container terminates or restarts, kubelet keeps its logs on the node. To prevent these files from consuming all of the host’s storage, a log rotation mechanism should be set on the node.
You can use kubectl logs to retrieve logs from a previous instantiation of a container with --previous flag, in case the container has crashed.
If you want to take a look at additional logs. For example, in Linux journald logs can be retrieved using the journalctl command:
$ journalctl -u docker
You can implement cluster-level logging and expose or push logs directly from every application but the implementation for such a logging mechanism is not in the scope of Kubernetes.
Also there are many tools offered for Kubernetes for logging management and aggregation - see: logs-tools.