Container technology has gained traction in industrial use for its scalability and lightweight virtualization, especially in cloud environments. Nevertheless, research has shown that containerized applications are an appealing target for cyberattacks, which may lead to interruption of business-critical services and financial damage. State-of-the-art anomaly-based host intrusion detection systems (HIDS) may enhance the runtime security for containers. However, they were not designed to deal with the characteristics of containerized environments. Specifically, they cannot effectively cope with the scalability of containers and the diversity of anomalies. To address these challenges, we introduce a novel anomaly-based HIDS that relies on monitoring heterogeneous properties of system calls. Our key idea is that anomalies can be accurately detected when those properties are examined jointly within their context. For this reason, we model system calls leveraging a graph-based structure that emphasizes their dependencies within their relative context, allowing us to precisely discern between normal and malicious activities. We evaluate our approach on two datasets of 20 different attack scenarios containing 11,700 normal and 1,980 attack system call traces. The achieved results show that our solution effectively detects various anomalies with reasonable runtime overhead, outperforming state-of-the-art tools.