private void addIndexingChainsTo(ContainerCluster<?> indexer, Content content, IndexingDocproc indexingDocproc) {
            addIndexingChain(indexer);
            DocprocChain indexingChain;
            ComponentRegistry<DocprocChain> allChains = indexer.getDocprocChains().allChains();
            if (indexingDocproc.hasExplicitChain() && !indexingDocproc.getChainName().equals(IndexingDocprocChain.NAME)) {
                indexingChain = allChains.getComponent(indexingDocproc.getChainName());
                if (indexingChain == null) {
                    throw new IllegalArgumentException(content.getCluster() + " refers to docproc " +
                                                       "chain '" + indexingDocproc.getChainName() +
                                                       "' for indexing, but this chain does not exist");
                }
                else if (indexingChain.getId().getName().equals("default")) {
                    throw new IllegalArgumentException(content.getCluster() + " specifies the chain " +
                                                       "'default' as indexing chain. As the 'default' chain is run by default, " +
                                                       "using it as the indexing chain will run it twice. " +
                                                       "Use a different name for the indexing chain.");
                }
                else {
                    checkThatExplicitIndexingChainInheritsCorrectly(allChains, indexingChain.getChainSpecification());
                }
            } else {
                indexingChain = allChains.getComponent(IndexingDocprocChain.NAME);
            }

            indexingDocproc.setChain(indexingChain);
        }
Select/creates and initializes the indexing cluster coupled to this
config-model/src/main/java/com/yahoo/vespa/model/content/Content.java