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Tools for Troubleshooting

This chapter is about tools for troubleshooting kubernetes.

Essential tools

  • kubectl: for interacting with kubernetes cluster, e.g. kubectl describe pod <pod-name>
  • journalctl：for viewing logs, e.g. journalctl -u kubelet -l
  • iptables and ebtables：for debugging service problems, e.g. iptables -t nat -nL checks whether kube-proxy's iptables rules are expected
  • tcpdump：for debugging network problems, e.g. tcpdump -nn host 10.240.0.8
  • perf: for debugging performance issues, e.g. troubleshooting issues like Container Isolation Gone Wrong

sysdig

sysdig is a container troubleshooting tools, which provides both opensource and commercial products. For regular troubleshooting, I believe opensourced version is enough.

On top of sysdig, you can also use csysdig and sysdig-inspect as command line interface and GUI.

Setup

# on Ubuntu
curl -s https://s3.amazonaws.com/download.draios.com/DRAIOS-GPG-KEY.public | apt-key add -
curl -s -o /etc/apt/sources.list.d/draios.list http://download.draios.com/stable/deb/draios.list
apt-get update
apt-get -y install linux-headers-$(uname -r)
apt-get -y install sysdig

# on REHL
rpm --import https://s3.amazonaws.com/download.draios.com/DRAIOS-GPG-KEY.public
curl -s -o /etc/yum.repos.d/draios.repo http://download.draios.com/stable/rpm/draios.repo
rpm -i http://mirror.us.leaseweb.net/epel/6/i386/epel-release-6-8.noarch.rpm
yum -y install kernel-devel-$(uname -r)
yum -y install sysdig

# on MacOS
brew install sysdig

Examples

# Refer https://www.sysdig.org/wiki/sysdig-examples/.
# View the top network connections
sudo sysdig -pc -c topconns
# View the top network connections inside the wordpress1 container
sudo sysdig -pc -c topconns container.name=wordpress1

# Show the network data exchanged with the host 192.168.0.1
sudo sysdig fd.ip=192.168.0.1
sudo sysdig -s2000 -A -c echo_fds fd.cip=192.168.0.1
 
# List all the incoming connections that are not served by apache.
sudo sysdig -p"%proc.name %fd.name" "evt.type=accept and proc.name!=httpd"

# View the CPU/Network/IO usage of the processes running inside the container.
sudo sysdig -pc -c topprocs_cpu container.id=2e854c4525b8
sudo sysdig -pc -c topprocs_net container.id=2e854c4525b8
sudo sysdig -pc -c topfiles_bytes container.id=2e854c4525b8

# See the files where apache spends the most time doing I/O
sudo sysdig -c topfiles_time proc.name=httpd

# Show all the interactive commands executed inside a given container.
sudo sysdig -pc -c spy_users 

# Show every time a file is opened under /etc.
sudo sysdig evt.type=open and fd.name

# View the list of processes with container context
sudo csysdig -pc

More usages could be found at Sysdig User Guide.

Weave Scope

Weave Scope is another container monitoring and troubleshooting tool. Compared to sysdig, it provides a simple GUI which describes the entire topology of the cluster.

Weave Scope consists of two components: the app and the probe. The components are deployed as a single Docker container using the scope script. The probe is responsible for gathering information about the host on which it is running. This information is sent to the app in the form of a report. The app processes reports from the probe into usable topologies, serving the UI, as well as pushing these topologies to the UI.

                    +--Docker host----------+      +--Docker host----------+
.---------------.   |  +--Container------+  |      |  +--Container------+  |
| Browser       |   |  |                 |  |      |  |                 |  |
|---------------|   |  |  +-----------+  |  |      |  |  +-----------+  |  |
|               |----->|  | scope-app |<-----.    .----->| scope-app |  |  |
|               |   |  |  +-----------+  |  | \  / |  |  +-----------+  |  |
|               |   |  |        ^        |  |  \/  |  |        ^        |  |
'---------------'   |  |        |        |  |  /\  |  |        |        |  |
                    |  | +-------------+ |  | /  \ |  | +-------------+ |  |
                    |  | | scope-probe |-----'    '-----| scope-probe | |  |
                    |  | +-------------+ |  |      |  | +-------------+ |  |
                    |  |                 |  |      |  |                 |  |
                    |  +-----------------+  |      |  +-----------------+  |
                    +-----------------------+      +-----------------------+

Setup

kubectl apply -f "https://cloud.weave.works/k8s/scope.yaml?k8s-version=$(kubectl version | base64 | tr -d '\n')&k8s-service-type=LoadBalancer"

Access GUI

kubectl -n weave get service weave-scope-app

Pod details

Known Issues

When running scope on Ubuntu kernel 4.4.0 with option --probe.ebpf.connections (default is enabled), Node may panic because of a kernel issue:

[ 263.736006] CPU: 0 PID: 6309 Comm: scope Not tainted 4.4.0-119-generic #143-Ubuntu
[ 263.736006] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090007 06/02/2017
[ 263.736006] task: ffff88011cef5400 ti: ffff88000a0e4000 task.ti: ffff88000a0e4000
[ 263.736006] RIP: 0010:[] [] bpf_map_lookup_elem+0x6/0x20
[ 263.736006] RSP: 0018:ffff88000a0e7a70 EFLAGS: 00010082
[ 263.736006] RAX: ffffffff8117cd70 RBX: ffffc90000762068 RCX: 0000000000000000
[ 263.736006] RDX: 0000000000000000 RSI: ffff88000a0e7cd8 RDI: 000000001cdee380
[ 263.736006] RBP: ffff88000a0e7cf8 R08: 0000000005080021 R09: 0000000000000000
[ 263.736006] R10: 0000000000000020 R11: ffff880159e1c700 R12: 0000000000000000
[ 263.736006] R13: ffff88011cfaf400 R14: ffff88000a0e7e38 R15: ffff88000a0f8800
[ 263.736006] FS: 00007f5b0cd79700(0000) GS:ffff88015b600000(0000) knlGS:0000000000000000
[ 263.736006] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 263.736006] CR2: 000000001cdee3a8 CR3: 000000011ce04000 CR4: 0000000000040670
[ 263.736006] Stack:
[ 263.736006] ffff88000a0e7cf8 ffffffff81177411 0000000000000000 00001887000018a5
[ 263.736006] 000000001cdee380 ffff88000a0e7cd8 0000000000000000 0000000000000000
[ 263.736006] 0000000005080021 ffff88000a0e7e38 0000000000000000 0000000000000046
[ 263.736006] Call Trace:
[ 263.736006] [] ? __bpf_prog_run+0x7a1/0x1360
[ 263.736006] [] ? update_curr+0x79/0x170
[ 263.736006] [] ? update_cfs_shares+0xbc/0x100
[ 263.736006] [] ? update_curr+0x79/0x170
[ 263.736006] [] ? dput+0xb8/0x230
[ 263.736006] [] ? follow_managed+0x265/0x300
[ 263.736006] [] ? kmem_cache_alloc_trace+0x1d4/0x1f0
[ 263.736006] [] ? seq_open+0x5a/0xa0
[ 263.736006] [] ? probes_open+0x33/0x100
[ 263.736006] [] ? dput+0x34/0x230
[ 263.736006] [] ? mntput+0x24/0x40
[ 263.736006] [] trace_call_bpf+0x37/0x50
[ 263.736006] [] kretprobe_perf_func+0x3d/0x250
[ 263.736006] [] ? pre_handler_kretprobe+0x135/0x1b0
[ 263.736006] [] kretprobe_dispatcher+0x3d/0x60
[ 263.736006] [] ? do_sys_open+0x1b2/0x2a0
[ 263.736006] [] ? kretprobe_trampoline_holder+0x9/0x9
[ 263.736006] [] trampoline_handler+0x133/0x210
[ 263.736006] [] ? do_sys_open+0x1b2/0x2a0
[ 263.736006] [] kretprobe_trampoline+0x25/0x57
[ 263.736006] [] ? kretprobe_trampoline_holder+0x9/0x9
[ 263.736006] [] SyS_openat+0x14/0x20
[ 263.736006] [] entry_SYSCALL_64_fastpath+0x1c/0xbb

To fix this issue, you could either

  • Disable eBPF connections, e.g. --probe.ebpf.connections=false
  • Or, upgrade kernel to 4.13.0

References