Senior Network Security Engineer, Network Security Engineering Group - Security Engineering Section (RMI Security Eng. & Ops Dep)

Job Description:

About Organization

Security Engineering & Operations Department supports Rakuten Mobile and related services by providing robust security infrastructure, network security, identity/access management, and security operations platforms. As our business scales, ensuring secure and reliable operations across on-premises, cloud, and Kubernetes environments is mission-critical.

To support Rakuten Mobile’s rapid growth, we are continuously expanding our Linux/Kubernetes-based platforms and enhancing our authentication and secrets management capabilities. We are seeking an experienced engineer with 8+ years of hands-on expertise to accelerate stable operations, drive standardization, and elevate the security quality of our mission-critical infrastructure. The Network Security Engineering Section designs and operates secure network services using an advanced technology stack including Linux, RHEL, Kubernetes, IPA/FreeIPA, and Vault.

Job Duties

• Linux Infrastructure: Design, build, operate, and troubleshoot Red Hat Enterprise Linux and diverse Linux environments.
• Kubernetes Security: Securely operate, configure, and optimize Kubernetes clusters and related components to meet growing operational demands.
• Identity & Access Management: Manage authentication, user lifecycle, authorization, and policies using IPA/FreeIPA.
• Secrets & Certificate Management: Design and operate secrets management, PKI/certificate management, and access control using HashiCorp Vault or equivalent tools.
• Security Hardening: Perform security hardening, patch management, and audit support for Linux/Kubernetes environments to ensure high security standards.
• Automation: Drive configuration management, automation, and standardization using tools such as Ansible to improve operational efficiency.
• Incident Management: Handle incidents, conduct root-cause analysis (RCA), and implement preventive measures for mission-critical services.
• Cross-functional Collaboration: Work closely with network, cloud, security, and operations teams, utilizing English for technical communication and project coordination in a global environment.

Minimum Qualifications

• 8+ years of hands-on experience designing, building, and operating Linux/RHEL environments.
• Proven experience in operating, configuring, and troubleshooting Kubernetes environments.
• Practical experience with authentication platforms (IPA/FreeIPA), including user and authorization management.
• Practical experience with secrets management, certificate management, and access control (Vault or equivalent).
• Strong background in Linux security hardening, patch management, and vulnerability remediation.
• Fundamental knowledge of networking, DNS, TLS/PKI, firewalls, and load balancers.
• Strong analytical skills to independently handle incidents, analyze root causes, and improve operational processes.
• Professional proficiency in English (technical documentation, communication, and collaboration).

Preferred Qualifications

• Experience operating large-scale telecommunications, cloud, or mission-critical infrastructure.
• Automation experience using Ansible, Terraform, Python, or Shell scripting.
• Deep knowledge of Kubernetes security (RBAC, NetworkPolicy, container image management).
• Experience with monitoring, log analysis, SIEM integration, and incident response workflows.
• Relevant certifications such as RHCE, CKA, CKS, or other security-related credentials.
• Experience driving projects within global teams and managing multiple stakeholders.

Work Environment

• Department: Network Security Engineering Section, Security Engineering Department.
• Collaboration: Work alongside global teams with diverse backgrounds in Linux, networking, security, cloud, and Kubernetes.
• Stack: RHEL, Kubernetes, IPA/FreeIPA, Vault, Ansible, Git, CI/CD, and various monitoring/logging tools across on-premises and cloud environments.

Languages: