The answer is to restart the Docker daemon with `systemctl restart docker`. This error occurs because a system update often restarts or modifies the iptables service, which clears the custom Docker chains (like DOCKER and DOCKER-USER) that the daemon creates for container network isolation. When Docker tries to add a new rule to a missing chain, it fails with the “No chain/target/match by that name” message. Restarting the daemon forces it to rebuild all its iptables rules from scratch, restoring external connectivity to the front-end container. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of Docker’s reliance on iptables for port mapping and the impact of service dependencies during updates. A common trap is to manually re-add iptables rules or restart the iptables service, but Docker’s own restart is the clean fix. Memory tip: when Docker’s chains vanish, just “restart the daemon to reignite the firewall rules.”
XK0-005 Scripting, Containers and Automation Practice Question
This XK0-005 practice question tests your understanding of scripting, containers and automation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are a Linux administrator at a company that runs a web application in Docker containers on a single host. The application consists of a front-end container (nginx) and a back-end container (node.js). Recently, after a system update, the front-end container fails to start with the error: 'Error response from daemon: driver failed programming external connectivity on endpoint frontend: (iptables failed: iptables --wait -t filter -A DOCKER ! -i docker0 -o docker0 -p tcp -d 172.17.0.2 --dport 80 -j ACCEPT: iptables: No chain/target/match by that name)'. Which action should you take to resolve the issue?
Restart the Docker daemon with systemctl restart docker
Restarting Docker recreates its iptables chains and rules, fixing the missing chain error.
B
Reinstall iptables
Why wrong: Reinstalling iptables is unnecessary and may disrupt critical firewall rules; Docker normally manages its own rules.
C
Change the network driver to macvlan
Why wrong: Changing the driver is a workaround that avoids the issue but is not the recommended fix; it may also introduce other networking complications.
D
Update the kernel to the latest version
Why wrong: The issue is not kernel-related; a kernel update is unlikely to fix missing iptables chains and may introduce instability.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Restart the Docker daemon with systemctl restart docker
The error indicates that the Docker daemon's iptables rules are corrupted or missing, often caused by a system update that restarted or modified the iptables service. Restarting the Docker daemon with `systemctl restart docker` forces Docker to reinitialize its iptables chains (e.g., DOCKER, DOCKER-USER) and reapply the necessary rules, resolving the connectivity failure.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Restart the Docker daemon with systemctl restart docker
Why this is correct
Restarting Docker recreates its iptables chains and rules, fixing the missing chain error.
Related concept
Read the scenario before looking for a memorised answer.
✗
Reinstall iptables
Why it's wrong here
Reinstalling iptables is unnecessary and may disrupt critical firewall rules; Docker normally manages its own rules.
✗
Change the network driver to macvlan
Why it's wrong here
Changing the driver is a workaround that avoids the issue but is not the recommended fix; it may also introduce other networking complications.
✗
Update the kernel to the latest version
Why it's wrong here
The issue is not kernel-related; a kernel update is unlikely to fix missing iptables chains and may introduce instability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the misconception that iptables itself is broken or needs reinstallation, when the real issue is that Docker's custom iptables chains were lost and need to be recreated by restarting the Docker daemon.
Detailed technical explanation
How to think about this question
Docker uses iptables rules to manage port mapping and container connectivity on the default bridge network. The DOCKER chain in the filter table is dynamically created by the Docker daemon at startup; if iptables is flushed or restarted (e.g., after a system update that restarts iptables.service), the chain disappears, causing the 'No chain/target/match by that name' error. Restarting Docker regenerates these chains without requiring a full system reboot.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Scripting, Containers and Automation — This question tests Scripting, Containers and Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Restart the Docker daemon with systemctl restart docker — The error indicates that the Docker daemon's iptables rules are corrupted or missing, often caused by a system update that restarted or modified the iptables service. Restarting the Docker daemon with `systemctl restart docker` forces Docker to reinitialize its iptables chains (e.g., DOCKER, DOCKER-USER) and reapply the necessary rules, resolving the connectivity failure.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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