Service function chaining (SFC) is an emerging technique that provides steering of traffic flows through an ordered set of service functions (SFs). In SFC, high availability is one of the most important issues to be addressed. SF instances within the chain can become unavailable when SF instances are overloaded or failed (e.g., power outage). Therefore, in order to realize highly available SFC, load balancing and fault management for SF instances must be provided. In this paper, we propose an overload and failure management (OFM) module in SFC that consists of the overload management (OM) module and the failure management (FM) module. In the OM module, when the current load at an SF instance exceeds a low-level threshold, a backup SF instance is prepared in advance. Meanwhile, if the current load further exceeds a high-level threshold, flow migration from the current SF instance to the backup SF instance is triggered. The FM module detects the failure of the SF instance by using a failure alarm. Upon detecting the failure, flow migration to the backup SF instance is triggered. We implement the OFM module in OpenDaylight (ODL) and present the experimental validation results.